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

asp.net-mvc visual-studio asp.net-webpages
Paul Brown picture Paul Brown · Dec 14, 2011 · Viewed 19.8k times · Source

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 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\brownp\Documents\Visual Studio 2010\Projects\Cab\Cab\Models\AccountModels.cs 223 28 Cab

Also, every time I open the solution, it prompts me with the following:

VS2010 error when opening solution

I install via Web Platform Installer and it installs successfully however the message reappears every time I open the solution.

Can anyone offer any guidance?

Thanks Paul

Answer

Tom Stickel picture Tom Stickel · Mar 4, 2012

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 "/>

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