I have just upgraded one of our MVC applications to MVC2 and the .NET Framework 4 and I came accross the error message "Unrecognized attribute 'targetFramework'".

The fix for this is very straight forward. Since the application was previously built against the .NET framework 3.5 the application pool was correctly set to run against v2.0 of the .NET framework. When using .NET 4 the application pool needs to be set to run against v4 of the framework.