Metadata file dll could not be found

Question

I am working on a WPF  C  3 0 project  and I get this error   Error 1 Metadata file  WORK -  Tools VersionManagementSystem BusinessLogicLayer bin Debug  BusinessLogicLayer dll  could not be found C  - WORK -  Tools  VersionManagementSystem VersionManagementSystem CSC VersionManagementSystem   This is how I reference my usercontrols   xmlns vms  clr-namespace VersionManagementSystem   lt vms SignOffProjectListing Margin  5   gt    It happens after every failed build  The only way I can get the solution to compile is to comment out all my user controls and re-build the project  and then I uncomment the usercontrols and everything is fine   I have checked build orders and dependencies configurations   As you can see  it seems to have truncated the DLL file s absolute path    I have read that there is a bug with the length  Is this a possible problem   It s very annoying and having to comment  build  and uncomment  the build is becoming extremely tiresome

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In VS 2019  under the project References check if there are any unresolved items by expanding Analyzers     For me  there were two  dll files with wrong paths  Right click on each and select Remove     Build the project  then build the solution   Done

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In my case I got this error message for the simple reason that  after getting the latest version of the project from TFS  the wrong project in the solution was marked as the startup project  Choosing the correct project as the startup project solved this for me

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In my case  I have my installed directory in mistaken ways   If your solution path is something like  My Project 2c Very Popular 2c Unit Testing 2c Software and Hardware zip   it cannot resolve the metadata file  perhaps we should prevent some invalid words like  2c   Renaming the path into normal name resolved my issue

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For me the issue was that I had two Visual Studio windows opened  my project was running in debug in one window  and I tried to build it in another   I had to stop debugging and then it let me build successfully

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In my personal case  I had failed to add a reference to one of the projects in the solution and this is what was kicking up the error for me

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Closing and reopening Visual nbsp Studio nbsp 2013 worked for me

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Wow  it seems like this error can come from everywhere   Anyway  I added a new WebAPI controller to my MVC application and it automagically got all the references from NuGet  Little bit later I removed the references from the NuGet UI  but I forgot to delete the files using them  i e  System Http    For some reason  the error I was receiving was this  along with a simple warning about a variable not being used   I commented out the variable to get rid at least of the warning and rebuilding pointed me out of all the files that were using the non-existing reference  After deleting those files  everything went OK

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This issue can happen because you are using features that are not supported by the version of  net selected for the project   In my case the reason was I used    operator to check for null and throw exception   Strange enough that VS doesn t inform about the actual reason of the problem in the list of build errors   But you can find this information in the Output logs of the build

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In my case  the problem was caused by a simple build error      error CS0067  The event  XYZ  is never used   that  for any reason  did not show up in the error window   Because of that  the Visual Studio build system seemed to miss the error and tried to build dependent projects  which in turn failed with the annoying metadata message   The recommendation is -as stupid as it may sound-   First look at your Output Window   It took me half an hour before this idea hit me

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I got this problem in Visual nbsp Studio nbsp 2012 in a solution that had many projects  Rebuilding each project in the solution manually in the same order as the Project Build Order  right-click and rebuild in Solution Explorer  fixed it for me   Eventually I got to one that gave me a compile error  I fixed the error  and the solution would build correctly after that

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I saw this error because I had the following line in my code  looks like I was still thinking in SQL mode    if myVar is null      DoSomething      Visual studio  2017  reported no errors at design or compile time however the project would not build and gave the  missing  dll  error   Upon changing the erroneous line to   if myVar    null    The problem was resolved

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for me the problem occurred because I was in-lining variable   so the following does successful build   ReportCategory reportCategoryEnum  Enum TryParse reportCategory  true  out reportCategoryEnum     while when I modified my code as following  no errors were shown but build was failing   Enum TryParse reportCategory  true  out ReportCategory reportCategoryEnum

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Visual Studio 2019 this worked for me    Close Visual Studio  Delete the hidden  vs folder  Reopen Visual Studio and rebuild the solution

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If you have a space in your solution name  this will also cause the issue  Removing the space from your solution name  so path doesn t contain  20 will solve this

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I am running Visual nbsp Studio nbsp 2013   It appears that the build dependencies were incorrect  Deleting the   suo files did fix the problems I had

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I have agree all aboves just a difference  In my case  I am using Visual Studio 2019  I closed VS-2019 and opened with VS-2017  and rebuild the project everything working great  For whom in my position date is  4 19 2019

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For me it was wrong folder name  If you close from source that replaces spaces with   20   you will get such errors  Solution - just rename badly named folders

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I added a new project to my solution and started getting this     The reason  The project I brought in was targeting a different  NET framework  4 6 and my other two were 4 5 2

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In my case it was caused by a  NET Framework version mismatch   One project was 3 5 and the other referencing project 4 6 1

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I faced this problem  In my case I delete all bin and obj folders from all projects then this error will resolve for me  Try this for one more try to resolve the problem

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Navigate to Solution s Folder Explorer and delete the unused project folder that was throwing error  In my case  after deleting the project  the folder was still present in the directory  After deleting the folder solution built successfully

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Well  nothing in the previous answers worked for me  so it got me thinking about why am I clicking and hoping when as developers we should really try to understand what is going on here   It seemed obvious to me that this incorrect meta data file reference must be held somewhere   A quick search of the  csproj file showed the guilty lines  I had a section called  lt itemGroup  that seemed to be hanging onto the old incorrect filepath    lt ItemGroup gt       lt ProjectReference Include           MySiteOld MySite Entities MySite Entities csproj  gt           lt Project gt  5b0a347e-cd9a-4746-a3b6-99d6d010a6c2  lt  Project gt           lt Name gt Beeyp Entities lt  Name gt       lt  ProjectReference gt        So a simple fix really    Backup your  csproj file  Find the incorrect paths in the  csproj file and rename appropriately    Please make sure you backup your old  csproj before you fiddle

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As user  burzhuy points out  it can be important to look at the Outputwindow  and not just the Error List window   In my case I was working on making modifications to the Roslyn compiler  Its build projects run an extra check to see if the public fields are consistent with what has been defined as the compiler s public interface  otherwise it produces an RS0016 or RS0017 error  I had added a couple of public fields  and fixed the RS0016 error by hovering the mouse over the error and selecting  Add to public API    Later I changed my mind and moved the public fields to a different class  For some reason this produced the  Metadata file could not be found error   and the more I fiddled with it the more errors I got   You need to to find the correct PublicAPI Unshipped txtfile  in my case it was in E  Roslyn 32414 src Compilers Core Portable  and edit it manually to remove the lines that are no longer relevant

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I had a class in 4 6 1 refering an interface that was in 4 6 2    upgrading the class to 462 fixed it

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In my case inside my Web config file changing this    lt  xml version  1 0  encoding  utf-8   gt    to this   lt  xml version  1 0   gt    fixed my problem

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In my case I had this error because  one of my project used a different  NET framework version from the others of the solution  I used the NuGet packages manager to install NLog  so  i think  it installed for the  Net version of this project   I tried all solutions from this post  but none were working  I removed NLog  cleaned the solution and trid to compile  Same thing  CS006 error   It was when I deleted all files in obj Debug from this project that the solution compiled

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This error may be shown if you use fake assemblies  Removing fakes leads to successful build of the project

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In my case  setting the target framework solved the problem    Right click on the project and select Properties In Application  change Target framework to the same as the main project  e g    NET Framework 4 5

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This issue could occur due to a syntax error in your code that might not be visible to you because of the Meta Data error  So review your source file before doing any of the actions in previous answers

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None of the dozens of answers so far worked for me  In my case  I also got the error      Tuple element name  Value  is inferred  Please use language version 7 1 or greater to access an element by its inferred name   This appeared next to  Metadata file   dll  could not be found  errors on building  but it disappeared shortly after  as errors sometimes do as the IDE  catches up    Double clicking on the error to find it  and removing the offending code  fixes it   Otherwise  you can  try this in Visual Studio   Menu Project    lt Project name  Properties   Build   button Advanced   Language Version   C   lt latest minor version   e g   C  5 0    And that fixes it too   It looks like  Metadata file   dll  could not be found  is often a symptom of some other underlying problems  so if none of the top solutions work for you  check other errors and warnings and try to find the real issue

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None of the previous solutions worked for me so I ll share what did   I had this problem after merging some new class libraries from another branch which referred to each other  Deleting the references in the projects and recreating them finally fixed the problem  Apparently Visual Studio had merged over the wrong file paths

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Check the  csproj file of main project  Visual Studio does not clean that up in case you remove projects or alter references in the solution   I had old projects referenced three times in the  csproj file and compile showed this error to those removed projects

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I had this error when tried to publish my project   All answered above  not helped me     I just change my deploy and the publish successed

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I have found out that if you remove Microsoft CSharp assembly as a reference in the project  you will get this error

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In my case  these errors were caused by some corruption in the NuGet package manager  Subprojects of the solution were not getting built  but no errors were showing because of the metadata errors   Once all the NuGet packages were corrected  the project could build properly again

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In my case  I deleted the git folder and removed Git  Azure DevOps   This was the only method that I did that worked   I tried clean  rebuild  reconfigure build  deleting bin and obj folders  nothing worked  When I removed solution of Git  voil    It worked for me   I don t understand  but this solved it for me

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In my case  I solved this problem after noticing that I had referenced a  Net Framework 4 7 project as a dependency on a  Net Framework 4 6 1 project  After migrating project 4 7 to 4 6 1 my application compiled normally

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I had this error when I was trying to publish a web application  Turned out that one of a class properties was wrapped into   if DEBUG     public int SomeProperty   get  set     endif   but the property usage was not  The publishing was done in Release configuration without the DEBUG symbol  obviously

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The framework version of the current project differs from remaining projects  Change of framework version to existing projects version will resolve this

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In my case it was ReSharper being dumb and  even though my project targets C  nbsp 6 I was being offered refactorings to use C  nbsp 7-only features   For this reason I ended up changing this code   private DateTime   joinedDate   Column TypeName    DateTime2    public DateTime JoinedDate       get   return  joinedDate    DateTime Now        set    joinedDate   value        into this code   private DateTime   joinedDate   Column TypeName    DateTime2    public DateTime JoinedDate       get   gt   joinedDate    DateTime Now      set   gt   joinedDate   value      For some reason having the getter and setter using expression bodies made the compiler come up with that metadata error instead of a syntax error

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I ran into this error with Visual nbsp Studio nbsp 2015 when I removed the type annotation from a call to an extension method  which left only the empty angle brackets behind   So instead of obj extensionMethod lt Type gt    I had obj extensionMethod lt  gt      I would classify this as a bug in Visual Studio since I don t see how that mistake could produce that error

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I d faced the same problem  In my case I d referenced to a class library project with higher  Net version than my project and VS failed to build the project and raised the same error you posted    I simply set  Net version of my class library project the one that had broken the build  identical to the  Net version of referenced project and problem solved

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aaaaaand six years later during an upgrade to Visual Studio 2015 the same problem  Because this particular solution is not in this list I m adding to it   Two referenced dll s were in the c  windows system32    folder  Moving them to a non system folder and adding a reference to the new folder fixed it finally  The rest of the issues was indeed what others have said here already

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For my case it was that I had commented out classes in a specific  empty  namespace   namespace X Y Z W           Class code      When I removed the namespace code and the import  using  commands of it - it fixed the problem   In the build it was also saying - along with the missing DLL file of the project      error CS0234  The type or namespace name  W  does not exist in the namespace  X Y Z   are you missing an assembly reference

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Based on the error message I don t believe the file path is being truncated  It looks to just be incorrect  If I m reading the message correctly it appears to be looking for the DLL file at         WORK - Tools VersionManagementSystem BusinessLogicLayer bin Debug BusinessLogicLayer dll   This is not a valid path  Is it possible that you have a macro definition in the build process set to an invalid value

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In my case the issue was that I d manually deleted a non-compilation file which was marked as  missing    Once I deleted the reference to the now-missing file and recompiled - all was well

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The Visual Studio IDE doesn t do any building behind the scenes  the Msbuild application does   The VS IDE essentially just constructs the project file that is used by Msbuild and quite often it makes mistakes if you leave it up to the IDE to figure things out on it s own   If you are getting the Metadata file   dll  could not be found error it is likely due to the fact that the correct expected assemblies are not being found   So perhaps Visual Studio might be creating a project file for a 4 5 framework app  and expecting 4 5 assemblies  while you are referencing 4 0 assemblies   So look at your Visual Studio settings for incompatibilities or go into the project file yourself  and manually fix it by specifying the correct path  lt Reference Include  C   correct path to assembly  yourAssembly dll    gt

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I got the same error  Metadata file   dll  could not be found   and I tried several things described above  but the reason for the error was that I was referencing third-party DLL file which was targeting a  NET version higher that my project target  NET version  So the solution was to change the target framework of my project

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My issue came when i wrote c  7 code but the project was using older version for  net framework

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For me the following steps worked     Find the project that is not building Remove add references to projects within the solution

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When I did a build  it would usually show errors like this in Visual Studio 2017   Error   CS0006  Metadata file  C  src ProjectDir MyApp bin x64 Debug Inspection exe  could not be found MyApp   C  src ProjectDir MyApp CSC 1   Active   But sometimes an error like this would show for a couple seconds and then it would disappear and switch back to the above message   Error   CS1503  Argument 1  cannot convert from  MyApp Model Entities Asset  to  MyApp Model Model Entities Inspection  MyApp   C  src ProjectDir MyApp ViewModels AssetDetailsViewModel cs 1453    Active   So I spent time troubleshooting the first error but the real problem turned out to be due to the second error   First I had to delete all the  bin and  obj directories  then I also deleted the  suo files as indicated above   This allowed me to narrow down the problem to an interface issue   In my interface I had this       Task lt IList lt Defect gt  gt  LoadDefects Asset asset     But in my actual implementation I had this code       public virtual async Task lt IList lt Defect gt  gt  LoadDefects Inspection inspection               var results                             return results          The build completed successfully after I updated the interface to this       Task lt IList lt Defect gt  gt  LoadDefects Inspection inspection     So it seems like caching in VS caused it to keep showing the CS0006 error when the actual problem was the CS1503 error

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In my case some of the projects in the solution were targeted to Any CPU  some of them to x86  The compilation error disappeared after unifying the platform target across the solution

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It looks like such kind of errors related to the fact that Visual Studio doesn t provide correct information about an error  The developer doesn t even understand the reason for the failed build  It can be a syntax error or something else  In common  to solve such problems you should find the root of the problem  for example  look at the build log    In my case the problem was in fact that the Error List window didn t show any errors  But really there were syntax errors  I found these errors in the Output window  and after fixing them  the problem was solved

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I too had the same error  It hides as in the below path  The path which I referred to for the DLL file is like  D  Assemblies Folder Assembly1 dll    But the original path in which the assembly referred was  D  Assemblies 20Folder Assembly1 dll    Due to this path name variation  the assembly could not be retrieved from its original path and hence throws the  Metadata not found  error   The solution is in Stack Overflow question How do I replace all the spaces with  20 in C

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I had an quite unusual case of this error  but maybe someone would benefit from it   I had this error with missing  dll file of one of projects in solution  with target framework netstandard 2 0  I m working on and at once error with reference  to Microsoft Office Interop Word  this project uses   This solution was cloned from git repository  and same solution compiled well for other people in my team   I tried every propsed solution for issue - restarting VS  computer  cleaning project  checking and unchecking build checkboxes  checking if build order is proper etc   I figured out that manifest of this project was not selected by default  dropdown of manifest in project properties was empty and disabled   Therefore I tried to add it  but nothing worked   At last I started comparing this project  csproj file with one in other  older version of this project  which compiled without problem  After a bit of usless tries I figured out  that path to Microsoft Office Interop Word is the same in both projects  even thought it was a relative path starting with lots of  go up  symbols          And not working project was one level lower than other   Adding one more  go up  symbol         in reference path to Microsoft Office Interop Word inside project  csproj file solved the issue   I have no idea why this path was created that way and doesn t update in my case  while it work properly for others in my team

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A lot of these answers sound like trial and error  In my case though  it was simple  the referenced dll was not found in that particular location    If you see the build errors  typically in this case  the build complains about many dlls  The key is to find the right dll that is missing  In my case  one of the projects in my solution had a direct dll reference instead of a project reference  So  I needed to build the project that outputs that dll before building the failing solution to make sure the failing solution finds the missing dll in that particular location   Wow   that was simple  but quite difficult to put it into words

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In my case it happened to me when I was referencing NuGet packages locally and moved their directory to somewhere else  I changed the path inside NuGet Config but unfortunately I discovered that I should change the  csproject files manually to update the reference path  but the error message CS0006 was way far from describing this problem  Generally it also happens when there is a reference to DLL that couldn t be found  to be able to identify issue search your references in the project with the problem you will find some references with warning icon associated with them  try fixing those and it should work as expected

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I also met this problem  Firstly you have to manually build you DLL project  by right-click  Build  Then it will work

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For me  it was trying to find a DLL in a path that used to contain the Project  but we d moved it to a new directory  The Solution had the correct path to the Project  but Visual Studio somehow kept looking in the old location   Solution  Rename each problem Project - just add a character or whatever - then rename it back to its original name   This must reset some global cache of some kind in Visual Studio  because this clears both this issue up and several like it  while things like Clean do not

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I had the same issue and another solution   The issue  One solution  multiple Projects  The main application that uses some of the other results failed  saying   CSC   error CS0006  Metadata file  C  Repos TheApplication TheApplicationCommon bin Debug TheApplication dll  could not be found  But actually this Project generated C  Repos TheApplication TheApplicationCommon bin Debug TheApplicationCommon dll Another project that also uses the same dll compiled flawlessly   Before I updated an internal NuGet-package that used PostSharp 3 x x x and now uses PostSharp 4 x x x  And my solution was to add this to my   csproj file    lt  xml version  1 0  encoding  utf-8   gt   lt Project ToolsVersion       gt     lt Import Project       Condition         gt     lt PropertyGroup gt               lt AssemblyName gt TheApplication lt  AssemblyName gt               lt SkipPostSharp gt True lt  SkipPostSharp gt   lt  -- This line -- gt     lt  PropertyGroup gt        Another Solution- Clean  another Solution- Rebuild and it works locally and on the build server   Hope it helps someone  The thread is old and quite long but this issue returns often and I didn t see this solution yet  Btw using Visual Studio 2017  15 8 x

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I had a merge conflict in one  csproj file and ended up with two copies of one build target     lt Compile Include  SystemCodes APSystemCodes cs    gt   After I eliminated the duplicate the build worked

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Deleting the bin obj folders and then rebuilding the project worked for me    In my case  what I believe happened was that I experienced a run time error the first time I built the project so my dll file was not not generated   This happened when referencing a project from another  The project I was referencing was the one with the issue

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I got the same error using Visual Studio 2019  After a closer look on what was going on in the background i found out there were errors on appended class libraries which in turn were not compiling correctly and throughing at the same time the error  quot Meta data file not found quot   Corrected the errors  compiled it again and all worked  In my case the answer was found on analysis of the output tab

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In my case  the parent folder of the solution had a  20 in the name  I renamed the parent folder by removing the  20 and the issue got fixed

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In my case it was that the dependor project  the project depending upon the one in the error message  was missing values in its  Assembly version  fields under the project s  Properties   Application   Assembly Information       I just added in the same numbers which were there for  File version   clicked  OK  and the compiler errors disappeared     It turns out that re-adding the AssemblyVersion then building the project again resulted in another error claiming that it was already present in the project   It was   Under the properties node of the project in Solution Explorer  there was a  SolutionVersionInfo cs  file which also contained an AssemblyVersion attribute - deleting this file from the project resolved this error

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I just had the same problem  Visual Studio isn t building the project that s being referenced   Written Instructions    Right click on the solution and click Properties  Click Configuration on the left  Make sure the check box under  Build  for the project it can t find is checked  If it is already checked  uncheck  hit apply and check the boxes again   Optional  You had to do it for both Release and Debug modes on the solution properties    Screen capture Instructions    They say a picture is worth a thousand words  Click on the GIF to zoom in  and hopefully it will be easy to follow

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Most of the methods explained here did not solved the problem for me   Finally  I fixed the problem by applying the following steps   1  Close Visual Studio  2  Delete all the contents in the bin folders of each project  3  Open solution and rebuild  Hope this helps

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I was pulling my hair out with this problem also  but after trying the previous answers the only thing that worked for me was to open each project in my solution 1 by 1 and build them individually   Then I closed Visual nbsp Studio nbsp 2013  reopened my solution and it compiled fine   It s strange  because if I clicked each project in my Solution Explorer and tried to build them that way  they all failed  I had to open them alone in their own solutions

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Very strange  I tried all the previous answers and unfortunately nothing worked in my case   I encountered two errors    Missing  dll file Method already defined at another place with the same parameters   I have cleared the second error first by removing the function which has been duplicated at another place   My first error - that is  dll file missing has solved it on its own   I want to say  if you have more than a single error along with the  dll missing file error  please try to solve the other errors first  Maybe the  dll error solves it on its own

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I had the same issue   In my case  the project would still build in release mode and it was just when I tried to build in debug that it failed   What I ended up doing to fix the issue was simply copy all of the dlls  and other files from my release folder  into my debug folder   After doing this for every project  the errors melted away

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The suggested answer did not work for me  The error is a decoy for another problem   I found out that I was targeting a slightly different version of  NET and this was flagged as a warning by the compiler  but it was causing building to fail  This should have been flagged as an error and not a warning

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For me it was an unused import  using ApsNetCore  on a Controller  Removed it  clean  rebuild it and it worked

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In my case  I had a bunch of other build errors as well  some simple type conversions  along with this one  I was scratching my head trying to solve this  and I wasn t focusing on the other errors   What finally solved my problem was that I fixed all the other build error and then I build again and it build successfully   So in case you have other build errors along with missing DLL file error  and nothing else is working for you then try to fix the other errors first and then build the solution again

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Just pointing out the blatantly obvious   if you don t have  Show output window when build starts  enabled  make sure you re noticing if your build is failing  small  build failed  error in lower left

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I got this issue after updating the dlls nuget    I could solve this manually by correcting the  csproj file  Mostly the version wasn t updated in the file   For example     lt Analyzer gt  Include     packages Microsoft CodeAnalysis   VersionCheckAnalyzer 2 9 1   analyzers dotnet Microsoft CodeAnalysis VersionCheckAnalyzer dll   gt    lt Analyzer gt  Include     packages Microsoft CodeAnalysis   VersionCheckAnalyzer 2 9 7   analyzers dotnet Microsoft CodeAnalysis VersionCheckAnalyzer dll   gt

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Right click on the solution and click Clean  Right click on the solution and click Rebuild

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I had the same issue in VS2019  Here is what you need to do    Push latest changes on some branch Delete the project Remove project from QuickStart - you can try to reference not existing project and it will ask you to remove Clone the project Run the project

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For me it occurred when I included a new project to a solution   Visual Studio automatically selects  NET framework 4 5    I changed to version  NET 4 5 2 like the other libraries  and it worked

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I faced this issue after getting latest  Team Foundation Server  TFS  command    After resolving the conflicts I found using a statement for a namespace that does not exist in the project   So I removed that using statement then clean and rebuild  and everything was OK

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I faced this problem  In my case multiple C  projects were referenced as DLL files  Any compile time error in a project which is used as a DLL file  in other projects  would result in a flood of errors  The reason is  the compile time error prevents the creation of the corresponding DLL file  and this results in a series of errors in projects which refer to the missing DLL file   Therefore when you rebuild in Solution Explorer  ignoring the trivial compile time errors   a bunch of  metadata file  dll could not be found  errors will occur  making you think what wrong you did other than a simple rebuild    If you are facing this problem  then the best solution is to clean the solution and then build each project one by one to figure out which project is initiating the error

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Removing the packages folder containing NuGet in the solution folder worked for me  After rebuilding everything worked again  Check References in the solution and check for references that have a yellow triangle   Example picture

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I had a similar problem when I decompiled a very old library  which was deployed in a production environment  but the source code was lost   I took  dll  decompiled and generated projects and solution  I was unable to build the solution due to several errors of this kind   Tips in previous answers did not help  but after a while I noticed missing references in some projects to several assemblies like System dll   Suppose there is project A dependent on project B  There was no reference to System dll in project B  but the error after build was like  Metadata file  B dll  could not be found    There was no error about missing System dll in project B   Adding reference on libraries like System dll in project B solved the problem   System Data  System DirectoryServices  etc

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Coming back to this a few years later  this problem is more than likely related to the Windows maximum path limit   Naming Files  Paths  and Namespaces  Maximum Path Length Limitation

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I started having this problem after changing the solution a lot  shelving the changes and undoing it   Only way to solve it was removing and adding again the mapping from TFS to my local folder

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The cause of the problem may be that you have mixed adding references to DLL files and projects in the solution   If you have projects A  B  and C    A references B and C as projects in the solution  B references C as a DLL file  reference to a file    You can build each project separately  but you can t rebuild a solution ending with  Metadata file  C dll  could not be found   Changing the reference from a file to a project in the solution helps

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My instance of the problem was caused by a common project that had a duplicate class name in it  under a different filename   It is strange that Visual Studio could not detect that and instead just blew up the build process

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I had this issue because  nuget NuGet exe was not included in my repository  Although I enabled DownloadNuGetExe in NuGet targets  it reported a proxy error when trying to download it  This caused the rest of the project builds to fail

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Well  my answer is not just the summary of all the solutions  but it offers more than that   Section  1    In general solutions   I had four errors of this kind     metadata file could not be found     along with one error saying  Source File Could Not Be Opened     Unspecified error         I tried to get rid of    metadata file could not be found    error  For that  I read many posts  blogs  etc  and found these solutions may be effective  summarizing them over here     Restart Visual Studio and try building again  Go to  Solution Explorer   Right click on Solution  Go to Properties  Go to  Configuration Manager   Check if the checkboxes under  Build  are checked or not  If any or all of them are unchecked  then check them and try building again  If the above solution s  do not work  then follow sequence mentioned in step 2 above  and even if all the checkboxes are checked  uncheck them  check again and try to build again  Build Order and Project Dependencies   Go to  Solution Explorer   Right click on Solution  Go to  Project Dependencies      You will see two tabs   Dependencies  and  Build Order   This build order is the one in which solution builds  Check the project dependencies and the build order to verify if some project  say  project1   which is dependent on other  say  project2   is trying to build before that one  project2   This might be the cause for the error  Check the path of the missing  dll   Check the path of the missing  dll  If the path contains space or any other invalid path character  remove it and try building again   If this is the cause  then adjust the build order      Section  2    My particular case   I tried all the steps above with various permutations and combinations with restarting Visual Studio a few times  But  it did not help me   So  I decided to get rid of other error I was coming across   Source File Could Not Be Opened     Unspecified error          I came across a blog post  TFS Error   Source File Could Not Be Opened     Unspecified error       I tried the steps mentioned in that blog post  and I got rid of the error  Source File Could Not Be Opened     Unspecified error       and surprisingly I got rid of other errors     metadata file could not be found     as well     Section  3    Moral of the story   Try all solutions as mentioned in section  1  above  and any other solutions  for getting rid of the error  If nothing works out  as per the blog mentioned in section  2  above  delete the entries of all source files which are no longer present in the source control and the file system from your  csproj file

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For me the problem was an error that didn t come up in the build output  namely I had two utility classes that were in different namespaces initially  I changed the namespace of the second one to match the first one s  without knowing there was another one utility class in the first one   and that s when this error started to come up    I imagine the build output error surfaced  because the Logic Layer library DLL file could not be built  and the main application couldn t find it   The solution was to change back the second utility class to a different namespace and that s when the real build errors started to pour in  After sorting them out the build went through just fine   As an overview  if any of the previous solutions doesn t work for you  you might have suppressed errors in the code that Visual Studio is not showing  so try to retrack your coding steps and check for any irregularities   PS  This was in Visual nbsp Studio nbsp 2015 Community Edition

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This can still happen in newer versions of Visual Studio  I just had it happen on Visual nbsp Studio nbsp 2013    Another thing to try is to close Visual Studio and delete the  suo file that is next to the  sln file   It will be re-generated the next time you Save all  or exit Visual Studio     I ve had this problem when adding new projects to the solution on another machine and then pulling the revisions in  but the  suo file can be corrupted in other cases as well and lead to very strange Visual Studio behaviour  so deleting it is one of the things I always try    Note that deleting the  suo file will reset the startup project s  of the solution   More on the  suo file is here

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This worked for me in VS2019  Net Core  ASP Net Core solution     Open a PowerShell console in the same location of the solution   Type dotnet restore to restore al packages and projects Type dotnet build  The solution will be built    Now it can be built also from Visual Studio IDE too   None of the other solution given worked for me

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I received this error after opening a project in which Entity Framework was referenced  so I deleted such references  and reinstalled Entity Framework version 6 0 0 0 through pthe acket manager this way   install-package entityframework -version 6 0 0 0   The error was still showing  so I thought that those references were there because there was an older version of Entity Framework supposedly  preinstalled  on the project  but it was not really working   So I went up to the file packages config and noticed that there was another reference    lt packages gt       lt package id  EntityFramework  version  5 0 0  targetFramework  net45    gt       lt package id  EntityFramework  version  6 0 0  targetFramework  net45    gt   lt  packages gt    Then I deleted the line  cleaned and rebuild the project and the container solution  and it finally worked

[c#] Metadata file '.dll' could not be found

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