The name 'ViewBag' does not exist in the current context

Question

I am trying to use ViewBag in my application, I have all of the recent dlls, the latest version of MVC 3, but yet I am still getting the Error:

"The name 'ViewBag' does not exist in the current context"

I have even uninstalled and then re-installed MVC 3 and yet there is no change.

Also, I do not believe that the dll's are showing up in the GAC.

What might be my problem? Or how to add the dll's to the GAC?