I am afraid I am not completely sure what lesson you mean - I assume that you meant the page 459 of our online tutorial here
but on this page there is a lesson for the RadTreeView control and not for the RadGrid.
About the namespaces - Telerik.WebControls is the namespace which is used with RadControls for ASP.NET and Telerik.Web.UI is the one which is used for RadControls for ASP.NET AJAX. Since I do not know what dll files you have in your Bin folder and how is your project configured I cannot tell what to do to solve the issue with the unrecognized namespace.
I think that the best way to proceed is that you prepare a sample, fully runnable demo which reproduces the problem, open a new support ticket and send it to us along with detailed explanation. Once we receive it, we will have a better understanding on your configuration and the issue and we will help you resolve the problem.
the Telerik team
Check out Telerik Trainer
, the state of the art learning tool for Telerik products.