.Net 4.0 introduces the concept of Client Profile. I came to know about it when I was adding references to my project file. Even though, I had added a few assemblies in the project reference, the compiler was complaining of not finding the namespaces in the references that I have added during compilation.
The project was a Windows Form Application. I opened up the Project Settings Page to see that the
Target Framework was .Net 4.0 Client Profile.
I changed it to .Net 4.0 Framework. Everything worked fine.
So to get past the error of missing namespaces, even though the assemblies having been added, check to make sure that the Target Framework is not in the Client Profile.
Raasukutty's 