这应该是一个比较老的问题。在.net 4 framework下，如果引用了.net 2的程序集，会有一个异常：
Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.
这时，在config文件中，加入一个带属性的startup区域就可以了：
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>
config文件整体上是这个样子：
<?xml version="1.0"?>
<configuration>
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>
<connectionStrings>
<add name="memberEntities" connectionString="metadata=res://*/member.csdl|res://*/member.ssdl|res://*/member.msl;provider=System.Data.SqlClient;provider connection string="data source=.\SQLEXPRESS;attachdbfilename=|DataDirectory|\member.mdf;integrated security=True;user instance=True;multipleactiveresultsets=True;App=EntityFramework"" providerName="System.Data.EntityClient" />
</connectionStrings>
</configuration>
<configuration>
<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>
<connectionStrings>
<add name="memberEntities" connectionString="metadata=res://*/member.csdl|res://*/member.ssdl|res://*/member.msl;provider=System.Data.SqlClient;provider connection string="data source=.\SQLEXPRESS;attachdbfilename=|DataDirectory|\member.mdf;integrated security=True;user instance=True;multipleactiveresultsets=True;App=EntityFramework"" providerName="System.Data.EntityClient" />
</connectionStrings>
</configuration>