Configuration error while using Areas in ASP.NET MVC 4

Question

After upgrading to ASP.NET MVC 4, application is breaking on accessing any webpage defined inside an Area

Description: An error occurred during the processing of a configuration file required to service this request. Please review the specific error details below and modify your configuration file appropriately.

Parser Error Message: An error occurred creating the configuration section handler for system.web.webPages.razor/host: The given assembly name or codebase was invalid. (Exception from HRESULT: 0x80131047)

<section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=__WebPagesVersion__.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />

Answer 1

Added this as an answer from comment:

Change Version=_WebPagesVersion_.0.0 to Version=2.0.0.0

Alternatively see if you have any other web.config files floating about in your project and see what values are used there - I understand that sometimes if you have multiple web.config referencing different version of the hosts section it can get quite upset. BTW there is no need to uninstall MVC 3 before 4 - they co-exist happily!

Answer 2

This is what worked for me: I had recently run Install-Package Microsoft.CodeDom.Providers.DotNetCompilerPlatform to install C#6 support for Razor, and I think it updated these libraries as well. The simple solution for me was to verify the version of the assembly in my references (there's a thought! lol). In my case, the assembly System.Web.WebPages.Razor had a "Version: 3.0.0.0" (right-click the assembly and select "Properties"). I believe whatever version is showing there, copy it over.

Before:

  <configSections>
    <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
      <section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
      <section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
    </sectionGroup>
  </configSections>

After:

  <configSections>
    <sectionGroup name="system.web.webPages.razor" type="System.Web.WebPages.Razor.Configuration.RazorWebSectionGroup, System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35">
      <section name="host" type="System.Web.WebPages.Razor.Configuration.HostSection, System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
      <section name="pages" type="System.Web.WebPages.Razor.Configuration.RazorPagesSection, System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" requirePermission="false" />
    </sectionGroup>
  </configSections>

Hope that helps someone else who ended up where I did. ;)