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

I was searching for a different issue and stumbled across this question, It is similar to a few I answered and figured I would post them here:

ModelClientValidationRule conflict

Build Errors - 'System.Web.Mvc.ModelClientValidationRule' Conflicts