Visual Studio 2013 C# Web Project builds but IDE reports The type or namespace name xxx could not be found error - asp.net-mvc-4

Question

When opening an MVC4 C# web project in Visual Studio 2013, the IDE reports the error "The type or namespace name '_' could not be found (are you missing a using directive or an assembly reference)", but the project builds and runs without any errors. Furthermore, intellisense does not include the project namespace.
The "missing" reference is to files within the same project.
for example; the web project namespace is "webproject.com", and references in a controller files to "webproject.com.models" is underlined in red with the error above.
I have checked the following:
All Solution projects are configured to use the same Target Framework(.Net 4)
web.config in the Views folder contains the namespace in the system.web.webPages.razor section
cleaned and rebuilt solution
deleted all bin and obj content
deleted .suo and .csproj.user files that were created by VS2010
The only way that I can get rid of these errors being reported in VS2013 is to unload then reload the project.
When opened in Visual Studio 2010 I do not get these problems.

Answer 1

I have the same issue.
ALthough the project compiles correctly, the code editor shows an error The type or namespace name '_' could not be found (are you missing a using directive or an assembly reference).
THere is one workaround. Just delete the *.SUO files and re-open the solution. THen for this only Session it works. Unfortunately after closing and reopening the solution the issue is back again. VS 2012 works fine.
Seems to be a bug in VS 2013....

Answer 2

My solution, when I encountered the problem with VS 2013 Express edition was to simply unload the offending project and reload. Opening the SUO or Project file and making changes had not affect.

Answer 3

Try to unload the project in VS2013, then right click the node and select edit "projectname.csproj". Check the individual references they might point to somewhere strange.
EDIT: the csproj file is an xml file and the references are located under Project -> ItemGroup -> Reference

Answer 4

I had the same issue.
It's a VS 2012 solution with different projects.
Search for all *.suo files and deleted them.
Rebuild and reopen Visual Studio.

Answer 5

There's a known issue with Web Application projects when bound to a TFS server that sounds like this issue. This occurs when the following TFS setting option is checked:
Options -> Source Control -> Environment -> Get everything when a solution or project is opened.
Disabling this option resolves the problem.
thanks,
Miguel Lacouture
[MSFT]

Answer 6

Same issue, on project reference.
I opened the referenced project file (*.csproj) with a text editor and did some cleanup:
1) reset these properties' values:
<PublishUrl>publish\</PublishUrl>
<InstallFrom>Disk</InstallFrom>
<UpdateEnabled>false</UpdateEnabled>
<IsWebBootstrapper>false</IsWebBootstrapper>
<TargetFrameworkProfile />
2) removed dirty platform/configurations:
<PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'x86|AnyCPU'">
...
<PropertyGroup Condition="'$(Configuration)|$(Platform)' == 'x86|x86'">
...
Now I can compile without any issue.
Glad to share it with you! :))

Answer 7

Same issue. Opening the project's properties and making a change to the name (or any value) and then rebuilding seems to have resolved it.

Answer 8

I have just had this problem and none of the solutions here helped. I fixed mine by doing a repair of Visual Studio (An option when you select to uninstall the program). Hope this helps someone

Answer 9

I had same issue when I added a new class file ( e.g. MyClass.cs) and called it in some other C# code places. For some reason VS did not add that new class file to my working project folder (not seen in VS, but seen in Windows File Explorer). And, hence, the compile path for new class file is not included in the compile section of my project file (e.g. MyProject.csproj). So to solve this problem, First, right click on your working project > Add > Existing Item ... > Select your new class > OK.
Then, check the project file (*.csproj) and make sure a new element is inserted in the compile section such as:
Finally, rebuild your project and the problem should be solved.
Another reason for this issue is the project, I had long ago with VS, is my other project was set up with Client Profile as its target framework. So, to solve the issue: Right click your project in VS > Properties > Application tab > make sure Target Framework option is not Client Profile. You should change all projects in your solution to the same framework version AND all of them must not have Client Profile option.

Answer 10

Microsoft just released a new security update to be automatically applied to machines configured to use Microsoft Update.
Unfortunately, some ASP.NET MVC 3 and 4 VS projects can no longer build after the update is applied. These projects will fail with the following error:
"Could not locate the assembly "System.Web.Mvc,Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35,processorArchitecture=MSIL"
My project also had the error "The type or namespace name 'System.Web.Mvc' could not be found (are you missing a using directive or an assembly reference)". Installing the latest version of Microsoft.AspNet.Mvc solved my problem. See the following article from Microsoft for more info:
http://blogs.msdn.com/b/webdev/archive/2014/10/16/microsoft-asp-net-mvc-security-update-broke-my-build.aspx

Answer 11

Unloading and then reloading the project worked for me.