Build Errors - 'System.Web.Mvc.ModelClientValidationRule' Conflicts - asp.net-mvc

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...
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-
Go to solution explorer
Reference
Right click on System.Web.WebPages
Remove
Now run your application and Enjoy !

Answer 5

This issue, which is the same as you described in VS2010, occurred in my case in VS2015 with a newer version of MVC (V5).
Here's how I was able to fix it:
Update the NUGET packages to the latest version.
In your project, remove the references for Microsoft.AspNet.WebPages. Then, re-add reference by using the latest package (use "Browse..."):
C:\Program Files (x86)\Microsoft ASP.NET\ASP.NET Web Pages\v2.0\Packages\Microsoft.AspNet.WebPages.2.0.30506.0\lib\net40
Ensure that all projects are referencing the same assembly, if not, fix them as described above. Then, re-build the solution. In my case, it fixed the error.
Check the Web.config file, and fix settings such as:
<appSettings>
<add key="webpages:Version" value="3.0.0.0" />
<add key="webpages:Enabled" value="true" />
...
<runtime>
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Web.WebPages" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.0" />
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="0.0.0.0-5.2.3.0" newVersion="5.2.3.0" />
</dependentAssembly>