- In the Solution Explorer, right click on the project that wont load and click on "Edit [ProjectName].csproj". This will open up the project definition file in VS. You can also edit this manually using your favorite text editor, opening the file through Windows Exporer.
- Find the line in the file that starts with
ProjectTypeGuids
and remove the entry "{E53F8FEA-EAE0-44A6-8774-FFD645390401}" from the list (this is code that tells Visual Studio that it is an MVC 3 project - for some reason, including this in the project file after installing MVC 4 messes things up). - Save the .csproj. file and [Reload] the project through the Right Click menu in Solution Explorer.
Error Loading MVC 3 Project after MVC 4 is Installed or in VS 2011
Since installing the ASP.net MVC 4 Beta, it has happened to me a few times that MVC 3 websites will not load when the solution is loaded into VS 2010 (I have also read about this happening with VS 2011).
You can fix this by doing the following: