ASP.NET MVC 4 breaks ASP.NET MVC 3 projects

Question

After installing the ASP.NET MVC 4 Developer Preview, I can no longer open MVC 3 projects, with the following error message:

The project type is not supporte         


        

Answer 1

ASP.NET MVC 4 Developer Preview runs side by side with previous versions of ASP.NET MVC, however there are a few known issues to be aware of. The biggest one:

Installing ASP.NET MVC 4 Developer Preview breaks ASP.NET MVC 3 RTM applications. ASP.NET MVC 3 applications that were created with the RTM release (not with the ASP.NET MVC 3 Tools Update release) require the following changes in order to work side-by-side with ASP.NET MVC 4 Developer Preview. Building the project without making these updates results in compilation errors.

You'll find the solutions here.