The type or namespace name could not be found

Question

I have a C  solution with several projects in Visual Studio 2010  One is a test project  I ll call it  PrjTest    the other is a Windows Forms Application project  I ll call it  PrjForm     There is also a third project referenced by PrjForm  which it is able to reference and use successfully   PrjForm references PrjTest  and PrjForm has a class with a using statement   using PrjTest     Reference has been correctly added using statement is correctly in place Spelling is correct PrjTest builds successfully PrjForm almost builds  but breaks on the using PrjTest  line with the error    The type or namespace name  PrjTest  could not be found  are you missing a using directive or an assembly reference    I ve tried the following to resolve this    Removed Resharper  since Resharper had no trouble recognizing the referenced project  I thought it might be worth a shot   Removed and re-added the reference and using statement Recreated PrjForm from scratch PrjForm currently resides inside the PrjTest folder  I tried moving it to an outside folder Loaded the solution on a different computer with a fresh copy of VS 2010   I have done my homework and spent far too long looking for an answer online  none of the solutions has helped yet   What else could I try

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I had the same issue  The target frameworks were fine for me  Still it was not working   I installed VS2010 sp1  and did a  Rebuild  on the PrjTest  Then it started working for me

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See this question   Turns out this was a client profiling issue   PrjForm was set to   Net Framework 4 Client Profile  I changed it to   Net Framework 4   and now I have a successful build   Thanks everyone   I guess it figures that after all that time spent searching online  I find the solution minutes after posting  I guess the trick is knowing the right question to ask

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PrjForm was set to   Net Framework 4 Client Profile  I changed it to   Net Framework 4   and now I have a successful build    This worked for me too  Thanks a lot  I was trying an RDF example for dotNet where in I downloaded kit from dotnetrdf   NET4 Client Profile  Always target NET4 Client Profile for all your client desktop applications  including Windows Forms and WPF apps    NET4 Full framework  Target NET4 Full only if the features or assemblies that your app need are not included in the Client Profile  This includes  If you are building Server apps  Such as    ASP Net apps Server-side ASMX based web services   If you use legacy client scenarios  Such as  o Use System Data OracleClient dll which is deprecated in NET4 and not included in the Client Profile    Use legacy Windows Workflow Foundation 3 0 or 3 5  WF3 0   WF3 5    If you targeting developer scenarios and need tool such as MSBuild or need access to design assemblies such as System Design dll

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The using statement refers to a namespace  not a project   Make sure that you have the appropriately named namespace in your referenced project   namespace PrjTest        public class Foo                     etc               Read more about namespaces on MSDN    Using Namespaces

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The compiled dll should have public Class

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It is also possible  that the referenced projects targets  NET 4 0  while the Console App Project targets  NET 4 0 Client Library    While it might not have been related to this particular case  I think someone else can find this information useful

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In my case I had   Referenced DLL    NET 4 5  Project    NET 4 0  Because of the above mismatch  the 4 0 project couldn t see inside the namespace of the 4 5  DLL  I recompiled the  DLL to target  NET 4 0 and I was fine

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Other problem that might be causing such behavior are build configurations   I had two projects with configurations set to be built to specific folders  Like Debug and Any CPU and in second it was Debug and x86   What I did I went to Solution- gt Context menu- gt Properties- gt Configuration properties- gt Configuration and I set all my projects to use same configurations Debug and x86 and also checked Build tick mark   Then projects started to build correctly and were able to see namespaces

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just changed Application s target framework to   Net Framework 4    And error got Disappeared   good luck   D

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I solved mine because the other project was coded with  NET 4 5 and the other one was coded 4 0

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For COM ActiveX references  VS 2012 will show this error right on using statement  Which is quite funny  since it s saying that may be you are missing a using statement    To solve this  register the actual COM ActiveX dll even if it s in the neighbor project  and add a reference through COM channel  not project channel  It will add Interop ProjectName instead of ProjectName as a reference and this solves this strange bug

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If your project  PrjTest  does not expose any public types within the PrjTest namespace  it will cause that error   Does the project  PrjTest  include any classes or types in the  PrjTest  namespace which are public

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Another thing that can cause this error is having NuGet packages that have been built with a newer version of  NET   The original error   frmTestPlanSelector cs 11 7   error CS0246  The type or namespace name  DatabaseManager   could not be found  are you missing a using directive or an assembly reference      Further up in the log I found this   C  Windows Microsoft NET Framework v4 0 30319 Microsoft Common targets 1605 5   warning MSB3275  The primary reference   redacted  DatabaseManager bin Release DatabaseManager dll  could not be resolved because it has an indirect dependency on the assembly  System Data SQLite  Version 1 0 94 0  Culture neutral  PublicKeyToken db937bc2d44ff139  which was built against the   NETFramework Version v4 5  framework  This is a higher version than the currently targeted framework   NETFramework Version v4 0    The solution was to re-install the NuGet packages   http   docs nuget org docs workflows reinstalling-packages

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check your Project Properties  your Reference Paths should be empty like this     Regards

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I encountered this issue it turned out to be   Project B references Project A   Project A compiled as A dll  assembly name   A    Project B compiled as A dll  assembly name A    Visual Studio 2010 wasn t catching this  Resharper was okay  but wouldn t compile  WinForms designer gave misleading error message saying likely resulting from incompatbile platform targets   The solution  after a painful day  was to make sure assemblies don t have same name

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Changing the framework to     NET Framework 4 Client Profile   did the job for me

[c#] The type or namespace name could not be found

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