asp.net mvc 4 - MVC 4 Beta side by side installation error

Question

I just installed the MVC 4 Beta now my MVC 3 application does not compile with the following error:

The type 'System.Web.Mvc.ModelClientValidationRule' exists in both 'c:Program Files (x86)Microsoft ASP.NETASP.NET MVC 3AssembliesSystem.Web.Mvc.dll' and 'c:Program Files (x86)Microsoft ASP.NETASP.NET Web Pagesv2.0AssembliesSystem.Web.WebPages.dll' C:UsersmichaeljoDocumentssrcpatientgivePhc.MvcInfrastructurePasswordStrengthAttribute.cs

It would appear this has been moved to a different assembly and since both assemblies are in the GAC it does not know which to use.

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

<Reference Include="System.Web.WebPages"/> 

To

<Reference Include="System.Web.WebPages, Version=1.0.0.0,
Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL "/>