[A]System.Web.WebPages.Razor. Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration. HostSection.

Problem:

[A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration.HostSection. Type A originates from 'System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' in the context 'Default' at location 'C:\Windows\Microsoft.Net\assembly\GAC_MSIL\
System.Web.WebPages.Razor\
v4.0_2.0.0.0__31bf3856ad364e35\
System.Web.WebPages.Razor.dll'.
Type B originates from 'System.Web.WebPages.Razor, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' in the context 'Default' at location 'C:\Users\RASIK\AppData\Local\Temp\Temporary ASP.NET Files\root\6c0b9ec1\5701cd39\assembly\
dl3\696206eb\f8e649c4_51b4d101
\System.Web.WebPages.Razor.dll'.

Solution:
I found the cause of this error that the web.config was referencing System.Web.WebPages.Razor, version=2.0.0.0. Later I changed it to System.Web.WebPages.Razor, version=3.0.0.0 it works fine problem was resolved.

If the following,  System.Web.WebPages.Razor is not present in webconfig add it.  

<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <assemblyIdentity name="System.Web.WebPages.Razor" publicKeyToken="31bf3856ad364e35" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-2.0.0.0" newVersion="3.0.0.0" />      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="DotNetOpenAuth.AspNet" publicKeyToken="2780ccd10d57b246" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-4.3.0.0" newVersion="4.3.0.0" />
      </dependentAssembly>
      <dependentAssembly>
        <assemblyIdentity name="DotNetOpenAuth.Core" publicKeyToken="2780ccd10d57b246" culture="neutral" />
        <bindingRedirect oldVersion="0.0.0.0-4.3.0.0" newVersion="4.3.0.0" />
      </dependentAssembly>
      <dependentAssembly> 
</assemblyBinding>