error message cs0012

 Compilation Error
Description: An error occurred during thecompilation of a resource required to service this request. Pleasereview the following specific error details and modify your source codeappropriately.

Compiler Error Message: CS0012: The type'System.Data.Objects.DataClasses.EntityObject' is defined in anassembly that is not referenced. You must add a reference to assembly 'System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c56sdf089'.

解决方法：

在<compilation></compilation> 之间加<add assembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>

如下：

<compilation debug="true" targetFramework="4.0">
            <assemblies>
                <add assembly="System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"/>
                <add assembly="System.Web.Abstractions, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
                <add assembly="System.Web.Routing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
                <add assembly="System.Web.Mvc, Version=2.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
            </assemblies>
        </compilation>