Razor 2 to Razor 3 MVC 5

Solution 1:

In your Web.config(-s) make sure assemblyBinding contains the proper version for the assembly System.Web.WebPages.Razor and System.Web.Mvc.

<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
  <dependentAssembly>
        <assemblyIdentity name="System.Web.WebPages.Razor" 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="1.0.0.0-5.0.0.0" newVersion="5.0.0.0" />
  </dependentAssembly>
</assemblyBinding>

And make sure that razor sectionGroup in ConfigSections reference latest versions as well:

<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>

Solution 2:

Check for version in web.config. If it again gives an error, try to clean the solution and rebuild it. Also check for project's Bin folder, removes old references from bin folder and rebuild the project solution.