当一个vs2010版本一下的项目转为2010项目时，会遇到这个错误：

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.

搜索下

解决方案如下：

<CONFIGURATION><STARTUP useLegacyV2RuntimeActivationPolicy="true"><SUPPORTEDRUNTIME version="v4.0"/><REQUIREDRUNTIME version="v4.0.20506"/></STARTUP>

</CONFIGURATION>

如果不行，修改如下：

<configuration><startup useLegacyV2RuntimeActivationPolicy="true"><supportedRuntime version="v4.0"/></startup></configuration>

至于为什么，帖一段e文的解释

：

After a bit of time (and more searching), I found this blog entry byJomoFisher.One of the recent problems we’ve seen is that, because of the support for side-by-side runtimes,.NET 4.0 has changed the way that it binds to older mixed-mode assemblies.These assemblies are,for example, those that are compiled from C++\CLI.Currently available DirectX assemblies are mixed mode.If you see a message like this then you know you have run into the issue:Mixed mode assembly is built against version 'v1.1.4322' of the runtime and cannot be loaded in the 4.0 runtime without additional configuration information.[Snip]The good news for applications is that you have the option of falling back to .NET 2.0 era binding for these assemblies bysetting an app.config flag like so:<startup useLegacyV2RuntimeActivationPolicy="true"><supportedRuntime version="v4.0"/></startup>So it looks like the way the runtime loads mixed-mode assemblies has changed. I can't find any details about this change, or why it was done. But the useLegacyV2RuntimeActivationPolicy attribute reverts back to CLR 2.0 loading.

解释的链接：http://stackoverflow.com/questions/1604663/what-does-uselegacyv2runtimeactivationpolicy-do-in-the-net-4-config

希望能够帮到你