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.NET\ASP.NET MVC 3\Assemblies\System.Web.Mvc.dll' and 'c:\Program Files (x86)\Microsoft ASP.NET\ASP.NET Web Pages\v2.0\Assemblies\System.Web.WebPages.dll' C:\Users\michaeljo\Documents\src\patientgive\Phc.Mvc\Infrastructure\PasswordStrengthAttribute.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 "/> 

Answer 2

Ok try this solution...

In the root Web.config file, add a new entry with the key webPages:Version and the value 1.0.0.0.

<appSettings> <add key="webpages:Version" value="1.0.0.0"/> <add key="webpages:Version" value="1.0.0.0"/> <add key="ClientValidationEnabled" value="true"/> <add key="UnobtrusiveJavaScriptEnabled" value="true"/> </appSettings> 

2.In Solution Explorer, right-click the project name and then select Unload Project. Then right-click the name again and select Edit ProjectName.csproj.

3.Locate the following assembly references:

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

Replace them with the following:

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

4.Save the changes, close the project (.csproj) file you were editing, and then right-click the project and select Reload.

REFERENCE

also try this

I Found this answer here for me the second edit combined with the first solved the problem.