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 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:

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 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...

1. 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: http://forums.asp.net/t/1723108.aspx/1

also try: http://www.asp.net/learn/whitepapers/mvc4-release-notes#_Toc303253815

Answer 3

Delete System.Web.WebPages from solution references. It is all.

Answer 4

The best way to avoid this conflict is-

1. Go to solution explorer
2. Reference
3. Right click on System.Web.WebPages
4. Remove

Now run your application and Enjoy !