开发环境一般引用的是本机 C:\Program Files (x86)\Microsoft ASP.NET\ASP.NET MVC 3\Assemblies下的System.Web.Mvc.dll，当系统更新时，此文件会更新为高级版本，从而和已经部署到服务器上的System.Web.Mvc.dll版本不一致。从能在线上运行时报下面的错误：

Assembly 'TestUnsafe, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' uses 'System.Web.Mvc, Version=3.0.0.1, Culture=neutral, PublicKeyToken=31bf3856ad364e35' which has a higher version than referenced assembly 'System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35'

发现没？System.Web.MVC的版本要求是3.0.0.1，而bin里放的仍然是3.0.0.0，肯定跑不起来。

OK，换个新的程序集上去，把System.Web.MVC.dll 3.0.0.1版放上去，仍然跑不起来，报错：

Parser Error Message: Could not load file or assembly 'System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)

这是由于Web.config未更新导致的，找到下面的几行：

  <runtime>    

 <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>  

</assemblyBinding>

  </runtime>

调整oldVersion和newVersion，改成：

  <runtime>     <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">       <dependentAssembly>         <assemblyIdentity name="System.Web.Mvc" publicKeyToken="31bf3856ad364e35" />         <bindingRedirect oldVersion="1.0.0.0-3.0.0.0" newVersion="3.0.0.1" />       </dependentAssembly>     </assemblyBinding>   </runtime>

看到没？把旧版本的MVC统一映射到3.0.0.1版去。再访问站点，一切正常了。