OK after hours of failing code. I created a new project and went step by step through your example on http://www.telerik.com/help/aspnet-ajax/window-getting-started.html
and it worked just fine.
What would prevent this from working on a website that I need to look for? The only difference from the example and my project is that I am trying to add this functionality to a user control called ucDocumentAccess.ascx and trying to open a web form called DocComments.aspx. Is there something special I need to do for a UC.