how to resolve this error?

[A]System.Web.WebPages.Razor.Configuration.HostSection cannot be cast to 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\Admin\AppData\Local\Temp\Temporary ASP.NET Files\root\a0e93667\bba50908\assembly\dl3\69851327\f1422f54_20f0ce01\System.Web.WebPages.Razor.dll'.