“System.IO.FileLoadException: Mixed mode assembly is built against version 'v2.0.50727' of the runtime and cannot be loaded in the 4.0 错误

最近在一个数据库测试项目中，遇到以下错误

Encountering “System.IO.FileLoadException: 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.”

网上很多方案说是在config里面加上

<startup useLegacyV2RuntimeActivationPolicy="true">
<supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.0"/>
</startup>

但是实际测试下来，这个只对非Test项目有效。对单元测试项目，解决方案为：

1，打开C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\CommonExtensions\Microsoft\TestWindow

2，找到vstest.executionengine.x86.exe.config

3，加上上面那个配置。

4，重启VS（不重启无效）。

来源：http://blog.kristandyson.com/2012/05/encountering-systemiofileloadexception.html