Microsoft.Web.UI.WebControls ????

I have been trying to use the treeview control using the microsoft web controls which I have downloaded but I always get this error:

File or assembly name Microsoft.Web.UI.WebControls, or one of its
dependencies, was not found.

Whats going on ?

Thanks in Advance

shouldnt that be System.Web.UI.WebControls?

Have you got Imports Microsoft.Web.UI.WebControls at the top of the page?
The above is correct as these are a seperate release from Microsoft and not part of the System Namespace but the Microsoft one.