Syed Aslam Basha here. I am a tester on the Information Security Tools Team.
At times I need to test an application with different versions of the .NET framework. You can configure the application config file to force the application to use the .NET version specified in the config file.
For example, suppose we have application built with .NET 3.5 and want to check the compatibility with .NET 4.0 follow the below steps;
3: <supportedRuntime version="v4.0.21006"/>
-Syed Aslam Basha (email@example.com)
Microsoft Information Security Tools (IST) Team