mvc3迁移到mvc4后，发布到服务器，出现了如下错误：
[A]System.Web.WebPages.Razor.Configuration.RazorPagesSection cannot be cast to [B]System.Web.WebPages.Razor.Configuration.RazorPagesSection. Type A From"System.Web.WebPages.Razor, Version=1.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"(In the context of"Default"In the"C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_1.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll"Position). Type B From"System.Web.WebPages.Razor, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35"(In the context of"Default"In the"C:\Windows\Microsoft.Net\assembly\GAC_MSIL\System.Web.WebPages.Razor\v4.0_2.0.0.0__31bf3856ad364e35\System.Web.WebPages.Razor.dll"Position).
看原因，可能是GAC程序集和当前程序集冲突的缘故，遂修改节点如下，添加了Syste.Web.WebPages.Razor的节点：
<assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
<dependentAssembly>
<assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35"/>
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="3.0.0.0"/>
</dependentAssembly>
<dependentAssembly>
<assemblyIdentity name="System.Web.WebPages.Razor" publicKeyToken="31bf3856ad364e35" />
<bindingRedirect oldVersion="1.0.0.0-2.0.0.0" newVersion="1.0.0.0" />
</dependentAssembly>
</assemblyBinding>
之后，注释掉web.config中所有的关于ext.net的节点配置。重新编译，启动服务器，正常运行。