Type or namespace name does not exist

Question

I have a WCF Data Service project built with Visual Studio 2010  which was working fine  All of a sudden  it didn t compile anymore  It was giving me messages like   Error 7   The type or namespace name  Services  does not exist in the namespace  System Data   are you missing an assembly reference      C  U   s Visual Studio 2010 Projects    DataService cs     Error  8   The type or namespace name  Linq  does not exist in the namespace  System   are you missing an assembly reference   DependencyResolver cs   3   14 Error  10  The type or namespace name  Web  does not exist in the namespace  System ServiceModel   are you missing an assembly reference   Error  12  The type or namespace name  DataService  could not be found  are you missing a using directive or an assembly reference    How can I fix it

User · Answer

I have experienced same problem with System.Data.SQLite. The source of the problem is the dll you have used should have same .NET version with your project.

For example if you have used (in my case) SQLite for .NET 4.5, your platform target should be .NET 4.5 too.

You can find platform target by: Project > (project name) Properties > Build.

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I had the same problem and tried all of the above without any success  then I found out what it was   I d created a folder called  System  in one of my projects and then created a class in it  The problem seems to stem from having a namespace called  System  when the  cs file is created  even if it is in a namespace of  MyProject System    Looking back I can understand why this would cause problems  It really stumped me at first as the error messages don t initially seem to relate to the problem

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I faced the same issue with an ASP NET MVC site when I tried to use LINQ to SQL  I fixed the problem by    Solution Explorer -  References -  Right-click on System Data Linq -  Copy Local  True

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I encountered this problem while using Visual Studio s Git integration to manage the project  For some reason the Windows Phone 8 project would compile just fine when targeting x86  but when I set it to target ARM  it would fail compiling with an error indicating that  Advertising  didn t exist in the Microsoft namespace   I ended up resolving the issue by removing the Microsoft Advertising   dll reference and adding it again

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I am referencing Microsoft CommerceServer Runtime Orders and experienced this error  This project is old and has Target framework  NET 2 0  In output I had this error   C  Windows Microsoft NET Framework v4 0 30319 Microsoft Common targets 1605 5   warning MSB3268  The primary reference  Microsoft CommerceServer Runtime  could not be resolved because it has an indirect dependency on the framework assembly  System Core  Version 3 5 0 0  Culture neutral  PublicKeyToken b77a5c561934e089  which could not be resolved in the currently targeted framework    NETFramework Version v2 0   To resolve this problem  either remove the reference  Microsoft CommerceServer Runtime  or retarget your application to a framework version which contains  System Core  Version 3 5 0 0  Culture neutral  PublicKeyToken b77a5c561934e089    I simply changed the target framework to  NET 4 and now it builds

User · Answer

I have had the same problem  and I had to set the  Target Framework  of all the projects to be the same  Then it built fine  On the Project menu  click ProjectName Properties  Click the compile tab  Click Advanced Compile Options  In the Target Framework  choose your desired framework

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In my case there was no change in projects  it just stopped to compile and with  type or namespace name XXX does not exist  and in the complaining class itself intellisense for that XXX namespace class works fine  The problem was in references indeed   Steps to reproduce    Solution has ProjectA  ProjectB   ProjectA references to third party log4net and it is marked Copy local  true  ProjectB references ProjectA and does not have reference to log4net   Solution compiles fine  Change in ProjectA  reference property for log4net to Copy local  false  Clean bin and obj folders  When you compile  ProjectA compiles but ProjectB complains about not finding ProjectA namespace    This is because ProjectB bin folder is missing third party library  log4net in my case    In this case solution would be -    make sure that third party libraries references are set to Copy local  true or  add path to such libraries in project properties under reference path

User · Answer

I found that this is caused by me having the same namespace name as class name  MyWorld MyWorld   Namespace ClassName     Change your namespace to a name that is not the same name as your class and this will compile   Source

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And if all else fails  such as ensuring that the target frameworks are the same  and you are dealing with a WPF class library in VS2010  simply restart Visual Studio   That did it for me

User · Answer

FOR ANYONE WITH LINKED FILES  I had this problem and was using silverlight and the offending file that was throwing this error was a linked file     The error from the compiler told me the error was happening in the project that the file lived in   It ended up that the error was NOT in that project  it was occurring in the project that contained the linked file   That project was missing a reference

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I experienced the same errors  After I discovered my project had the wrong Assembly name  I copied files from a different project and the namespaces got a little confused   and changed it back  the project compiled nicely

User · Answer

Delete the  refresh dll file if you are under source control  Then rebuild  It should work  This worked for me

User · Answer

I got a very similar error message that was caused by inadvertently having made a duplicate of a class in another project of my solution   Deleting the duplicate fixed the issue

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In my case the problem was happening because the class I created had a namespace that interfered with existing classes  The new class A had namespace zz yy xx  by mistake   References to objects in another namespace yy xx were not compiling in class A or other classes whose namespace was zz    I changed the namespace of class A to yy xx   which it should have been  and it started working

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Check to see that your target framework has the same  NET versions  I had the same problem and my class  NET was 3 5 and web solution had 4 5  I synchronised those  and then it worked

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I recently needed to do a System Restore and it caused several of my files to change disappear that I had been working on since the restore   Some of those were DLL files   I used Source Control to retrieve the entire project but I still had a similar issue as above   I found this answer that described you may need to remove a DLL and readd it to get your errors fixed   This was the case in my scenario     Removing WebMatrix WebData and readding it as well as adding in WebMatrix Data fixed my error of The type or namespace name  Data  does not exist in the namespace  WebMatrix

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I had an issue with System Linq not being recognized   The using statement had a red squiggly  etc   The way I solved it was to change my website to target dotnet 3 5  then switch back to the original targeted framework  4 0 in my case

[c#] Type or namespace name does not exist

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