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

Question

I am trying to \'build\' my MVC3 web app in VS2010 however keep getting the following error:

Error 2 The type \'System.Web.Mvc.ModelClientValidationRule\' exists

Answer 1

After installing MVC4 beta today, a few of my MVC 3 projects would not compile. (ModelClientValidationRule conflict) The fix was:

Edit:

ProjectName.csproj

Change

To