Where does error CS0433 Type X already exists in both A dll and B dll come from

Question

When I run a webapp from Visual Studio 2008 SP1 using the internal web server  not IIS  I receive the above mentioned error   The full error  source file Default aspx cs       Compiler Error Message  CS0433  The   type  WebApplication3 Site1  exists in   both    c  Windows Microsoft NET Framework v2 0 50727 Temporary   ASP NET   Files root aa563bcf 59deedc0 App Web site1 master cdcab7d2 muczzy9v dll    and    c  Windows Microsoft NET Framework v2 0 50727 Temporary   ASP NET   Files root aa563bcf 59deedc0 assembly dl3 44c3a3cf 80dd34ed 6968ca01 WebApplication3 DLL    The preceding full warning      Warning  CS0436  The type    WebApplication3  Default  in    c  Windows Microsoft NET Framework v2 0 50727 Temporary   ASP NET   Files root aa563bcf 59deedc0 App Web default aspx cdcab7d2  tlkwdos 0 cs    conflicts with the imported type    WebApplication3  Default  in    c  Windows Microsoft NET Framework v2 0 50727 Temporary   ASP NET   Files root aa563bcf 59deedc0 assembly dl3 44c3a3cf e096e61c 6568ca01 WebApplication3 DLL     Using the type defined in    c  Windows Microsoft NET Framework v2 0 50727 Temporary   ASP NET   Files root aa563bcf 59deedc0 App Web default aspx cdcab7d2  tlkwdos 0 cs     Source of warning points to an intermediate file App Web default aspx cdcab7d2  tlkwdos 0 cs   Line 162      Line 163      System Runtime CompilerServices CompilerGlobalScopeAttribute    Line 164     public class default aspx   global  WebApplication3  Default  System Web IHttpHandler   Line 165          Line 166         private static bool    initialized    and my question  where does this come from   The webapp  not website    has one Default aspx and one Site1 Master  no dependencies  They re almost empty  with an asp Label on the page  Previously  this webapp worked fine  When I remove any references in Default aspx cs to the master  all goes well  The master has some code only   It s actually one of many little fire-and-forget test webapps  so I couldn t care less  But I hadn t seen this before and now I m curious of what to do  other then copying code into a new project  cleaning solution doesn t help    Note  I ve read this post and some others  they don t apply

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I m converting an old asp net  v 1 or 2  web site to run under  net 4 5 as a web application    My solution was to move the user control event handler delegates that were causing the problem to a separate physical file     move this line to a new physical file  public delegate void LocationSearchedEventHandler  object sender     public partial class controls Drives LocationAddPanel   UserControl       public event LocationAddedEventHandler LocationAdded      protected virtual void OnLocationAdded LocationAddEventArg e

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I got re-directed here when clicking on the first Google hit when clicking on the error URL for CS0433  specifically      The type  Package  exists in both  Windows    Version N N N N  Culture neutral  PublicKeyToken null  ContentType Windows     and  Windows     Version 255 255 255 255  Culture neutral  PublicKeyToken null  ContentType Windows       Instead of outlining all the things I did to fix it  let me tell you what I did that broke it  I went to update the NuGet packages for a repo that needed a code update  The packages were pretty old  1 year or so  and all I initially tried to do was update it for a C  project   Sometime between starting that process and encountering this error  I somehow downgraded the version of the C   projects in that SLN to target 15063  I also noticed that the C  project had both the TargetPlatformMinVersion and TargetPlatformVersion newly set to 10 0 17134 0  The only thing I had to do to  fix  it was change the TargetPlatformMinVersion to a higher version than the TargetPlatformMinVersion for the C  project  Modifying the C   project to either version didn t change behavior  I m not sure why this suddenly stopped working but hopefully someone similarly blocked might get out of a pickle using similar strategies

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This may also happen if you have duplicate TagPrefix in your ASPX file   This would cause this error      lt    Register Src  Control1 ascx  TagName  Control1  TagPrefix  uc1    gt    lt    Register Src  Control2 ascx  TagName  Control2  TagPrefix  uc1    gt    You can fix this by simply changing the 2nd  uc1  to  uc2   Fixed      lt    Register Src  Control1 ascx  TagName  Control1  TagPrefix  uc1    gt    lt    Register Src  Control2 ascx  TagName  Control2  TagPrefix  uc2    gt

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Removing the class files from the App Code folder  and placing them directly under the website  solved this issue for me

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I had same issue with two ascx controls having same class name        Control1   lt    Control Language  C   ClassName  myClassName  AutoEventWireup  true        Control2   lt    Control Language  C   ClassName  myClassName  AutoEventWireup  true        I fixed it by simply renaming the class name      Control1   lt    Control Language  C   ClassName  myClassName1  AutoEventWireup  true        Control2   lt    Control Language  C   ClassName  myClassName2  AutoEventWireup  true

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For me at least  this happened when I removed a reference to an assembly and added a reference to a newer version of it  which had a different name  In this case  it seems that the old assembly remained in the bin and obj folder  and was not removed with the clean solution operation from Visual Studio  maybe because it is not part of the project anymore   In this case  it was enough to delete the contents of the bin and obj folders of the project where he error happens  from Windows Explorer  or a file management tool   Then  from Visual Studio  clean the solution and rebuild

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I have found another reason  different versions used for icons in toolbox and references in the project  After inserting the objects in some form  the error started

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This might happen if you place  cs files in App Code and changed their build action to compile in a Web Application Project   Either have the build action for the  cs files in App Code as Content or change the name of App Code to something else  I changed the name since intellisense won t fix  cs files marked as content   More info at http   vishaljoshi blogspot se 2009 07 appcode-folder-doesnt-work-with-web html

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This happened to me because of an error in my Web Config   lt add assembly  System Web Abstractions  Version 4 0 0 0  Culture neutral  PublicKeyToken 31BF3856AD364E35   gt   lt add assembly  System Web Helpers  Version 1 0 0 0  Culture neutral  PublicKeyToken 31BF3856AD364E35   gt   lt add assembly  System Web Routing  Version 4 0 0 0  Culture neutral  PublicKeyToken 31BF3856AD364E35   gt   lt add assembly  System Web Mvc  Version 5 1 0 0  Culture neutral  PublicKeyToken 31BF3856AD364E35   gt   lt add assembly  System Web WebPages  Version 3 0 0 0  Culture neutral  PublicKeyToken 31BF3856AD364E35   gt    The Sytem Web Helpers was pointed at 1 0 0 0 instead of 3 0 0 0  MVC 3 is being used on this project    Because IIS couldn t find the reference in the local folder it looked in the GAC and found two different versions  After pointing it at the correct reference IIS found the local dll and used that instead of searching the GAC

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Reference   https   support microsoft com en-in help 2028526 building-an-asp-net-project-in-visual-studio-results-in-compiler-error  When building an ASP NET project using Visual Studio  you may randomly see an error message similar to the following   Compiler Error Message  CS0433  The type  ASP summary common controls notes ascx  exists in both  c  Windows Microsoft NET Framework64 v2 0 50727 Temporary ASP NET Files Book Details abc12345 def8910 App Web msftx123 dll  and  c  Windows Microsoft NET Framework64 v2 0 50727 Temporary ASP NET Files Book Details abc12345 def8910 App Web msfty456 dll   Description  An error occurred during the compilation of a resource required to service this request  Please review the following specific error details and modify your source code appropriately       Source Error  Line 100                   Line 101    New Notes Line 102     Line 103    1450 Line 104                                Summary    Source File  d  http post publisher default aspx Line  102  Common scenarios where this error can occur are discussed below  Scenario 1  Description  A common cause is when there are two assemblies in the same web application bin folder containing two class definitions but that have the same class name  This can happen if more than one Default aspx was compiled into a single assembly  Commonly  this occurs when the Master page  Default master  and the Default ASPX page  Default aspx  both declare a  Default class   Solution  Change the class name of the master page  from  Default in most cases  and rebuild the project  It is important to resolve any naming conflict between classes    Scenario 2  Description  The Reference Paths in Visual Studio is used to specify the folder path for assembly references used by the project  It is possible that the path contains an assembly that contains the same class name  It may be that there are multiple References added to the same assembly  possibly different version or name  causing a naming conflict  Solution  Remove the old version reference  To do so  in Visual Studio right-click your web site and check the  References  in the properties   Scenario 3  Description  By default  when an ASP NET Web application is compiled the compiled code is placed in the Temporary ASP NET Files folder  By default the access permissions are given to the ASP NET local user account  which has the high-trust permissions needed to access compiled code  It is possible that there were some changes in the default permissions causing versioning conflicts  Another possibility would be that anti-virus software could be locking an assembly inadvertently  Solution  Clear the Temporary ASP NET Files Folder of all contents   Scenario 4  Description  When the batch attribute in the web config is set to True it eliminates the delay caused by the compilation required when you access a file for the first time  ASP NET precompiles all the un-compiled files in a batch mode  which causes delays the first time the files are compiled  Turning off batch compilation may expose masked compilation errors that may exist in the application but are not reported  However more importantly for this issue it tells ASP NET to dynamically compile individual  aspx  ascx files into separate assemblies instead of into a single assembly  Solution  Set batch false in the  section in web config  This should be considered a temporary solution as setting batch false in the compilation section has a significant performance impact on build times for the application in Visual Studio   Scenario 5  Description  Modifying the web config file for an ASP NET application or changing a file in the bin folder  such as adding  deleting  or renaming  causes the AppDomain to restart  When this occurs all session state is lost and cached items are removed from the cache as the website restarts  It is possible that the problem is caused by an inconsistent state in the web application  Solution  Trigger an AppDomain restart by touching  editing  the web config file   Scenario 6  Description  You can store source code in the App Code folder  and it will be automatically compiled at run time  The resulting assembly is accessible to any other code in the Web application  The App Code folder therefore works much like the Bin folder  except that you can store source code in it instead of compiled code  The class will be recompiled when there is a change in the source file  If there is conflict due to an outdated assembly then forcing a recompile may resolve the problem  Solution  Touch a file in the Bin or App Code folders to trigger a full recompilation

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This may happen when the same classname is specified in multiple  aspx cs files  i e  when two pages are created with different file name but by mistake have the same classname      file a aspx public partial class Test1  System Web UI Page     file b aspx public partial class Test1  System Web UI Page   While building the webapplication this gives a warning  but the application runs  however  after publishing the application doesn t work anymore and throws the exception as mentioned in the OP s question   Making sure that two classnames do no overlap solves the issue

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I ended up changing how the MasterType is referenced in the page mark up   I changed   lt    MasterType VirtualPath    x y MyMaster Master    gt  to  lt    MasterType TypeName  FullyQualifiedNamespace MyMaster    gt   See here for details   Hope this helps someone out

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There are quite a multiple of reasons for this  And most of the ones mentioned above apply to different scenarios  What I noted is that the error occurs ONLY when authentication is set to something else other than  None   For my testing purposes I will set this off and it works

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Theory  When this issue is not caused by a bug in the application  e g   duplicate class name    This issue appears to present after a change is made to the application s project that results in a new build  e g   code reference resource change   The issue appears to lie within the output of this new build  for various reasons Visual Studio is not replacing the entire contents of your application s obj bin folders  This results in at least some of the contents of your application s bin folder being out of date   When said issue occurs  clearing out the  Temporary ASP NET Files  folder  alone  does not solve the problem  It cannot solve the problem  because the stale contents of your application s bin folder are copied back into the  Temporary ASP NET Files  folder the next time your application is accessed  causing the issue to persist  The key is to remove all existing files and force Visual Studio to rebuild every object  so the next time your application is accessed the new bin files will be copied into the  Temporary ASP NET Files  folder   Solution   Close Visual Studio Perform an iisreset Delete all the folders and files within the  Temporary ASP NET Files  folder  the path is referenced in the error message  Delete the offending application s  obj  and  bin  folders Restart Visual Studio and open the solution Perform a  Clean Solution  followed by a  Rebuild Solution    Explanation   Steps 1-2  remove resource locks from the folders files we need to delete  Steps 3-4  remove all of the old build files Steps 5-6  create new versions of the build files

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In addition to trying 2Toad s answer  I also ended up having to close Visual Studio and delete my  vs folder   After that  everything built correctly   Incidentally  the error I was encountering didn t specify my Temp folder at all  but was referencing something else that was obviously system-generated   I neglected to save the specific error

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Look at the Inherits tag of all your aspx pages and master pages  Chances are there are two partial classes that have the same name  Change one and recompile   Here is some more info   http   blogs msdn com b carloc archive 2007 06 12 compiler-error-message-cs0433-in-asp-net-2-0 aspx

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Shut down w3svc and delete everything from c  Windows Microsoft NET Framework v2 0 50727 Temporary ASP NET Files root   added   on Windows 7  c  Users  username  AppData Local Temp Temporary ASP NET Files root  on IIS servers  64 bit  this can also occur  Look for   C  Windows Microsoft NET Framework64 v4 0 30319 Temporary ASP NET Files root   replace v4 0 30319 by the framework version you re using if newer on your server

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I still had the problem after all these suggestions  Some class inside App Code was being compiled to two DLL s  Something like this  simplified    warning CS0436  The type  HcmDbGeographyModelBinder  in     lt user profile dir gt  AppData Local Temp Temporary ASP NET Files temp 3b1ed8ee 11405e8e App Code oqr0kusq 0 cs    conflicts with the imported type  HcmDbGeographyModelBinder  in     lt user profile dir gt  AppData Local Temp Temporary ASP NET Files temp 3b1ed8ee 11405e8e assembly dl3 ea0aa3ee 6022e6d5 2cc8cf01 HCM Web Backoffice DLL     I just renamed the  App Code  folder to  Code   This is a MVC5 project  so there shouldn t be a problem with serving  cs files inside the web project s root

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I had the similar problem  This is my solution   Put isolated classes which require property  Build Action  set as  Compile  to any folder other than App Code like Application Code since the App Code folder will be compiled as a separate assembly  having the same Class compiled in 2 assemblies

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Close the Solution and re-open it  then check the projects references for doubling up     This can happen if you were using NuGet and changed the DLLs reference location  To fix it you have to manually edit the proj file removing the entries  eg      lt Import Project     packages CefSharp WinForms 53 0 0 build CefSharp WinForms targets  Condition  Exists     packages CefSharp WinForms 53 0 0 build CefSharp WinForms targets      gt    Watch out as these   lt Import  references can appear at different spots in the proj file

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if no other solution worked  then just rename the inherits class of that problem causing aspx file and aspx cs file to a new name  then rebuild the solution  then the issue will be solved for sure  this only worked for me  eg   in the aspx file do the following change the inherits class name to Defaultnew  lt    Page Title  quot  quot  Language  quot C  quot   MasterPageFile  quot   Main master quot  AutoEventWireup  quot true quot  CodeFile  quot Default aspx cs quot  Inherits  quot Defaultnew quot    gt   in the aspx cs file rename the class to the same as used in aspx file using System  using System Collections Generic  using System Web   public partial class Defaultnew   System Web UI Page

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Clean Solution  followed by  Rebuild Solution  seems to fix it as well

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In our case  the reason was a difference in the  dll versions of to sites in IIS  They are placed under each other in IIS  letting you access the other thru a subdomain  It inherits from the first web config  and combining that with the next web config  it failed  having different versions of mvc dll

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A super quick and handy fix is to abuse Visual Studio s incredible intellisense by temporarily referencing the class somewhere    Example   System Runtime CompilerServices ExtensionAttribute x   null    When building or hovering the cursor over the line you can view the following error       System Runtime CompilerServices ExtensionAttribute  exists in both    C  Program Files Reference Assemblies Microsoft Framework v3 5 System Core dll    This tells you the two sources causing the conflict immediately   System Core dll is the  dll file that you want to keep  so delete the other one    I found mine sitting in the bin directory  but it may be elsewhere in the project    As a matter of fact this is worth bearing in mind  because since the bin directory might not be included as part of the TFS change-set  it can explain why checking in your changes doesn t resolve the issue for other members of your team

[c#] Where does error CS0433 "Type 'X' already exists in both A.dll and B.dll " come from?

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