I have answered your ticket and I am pasting my response here in case anyone else has a similar question:
I am afraid some of the videos are no longer available. The ones that remain are here:http://www.telerik.com/videos/aspnet-ajax. The others have had no views and since most of the videos are outdated anyway, they have been removed.
What I can advise as a learning resource is the documentation (http://www.telerik.com/help/aspnet-ajax/introduction.html) and the demos of the controls (http://demos.telerik.com/aspnet-ajax/). The documentation has a common structure where you can navigate from the top to get familiar with the basics of the toolset and then each control has its own Getting Started article/section and more in-depth articles afterwards. The demos mostly showcase concrete features so you can see how to implement them, and they can also be a useful reference guide. You can also download them as a VS project from your account so you can examine/modify them locally.