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

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

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>

Answer 4

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

Answer 5

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 !