Hi Marin,
Thanks for your response!
Apparently, you did not look at my code that I had posted. If you did then you will notice that I have the VisibleOnPageLoad property set to false.
The link you provided for migrating onclientclick handlers helped resolve the issue of a window being opened upon loading the page and the issue of the window getting incorrect values passed to the page the window is loading. Once I corrected OnClientClicked method, added the AutoPostBack="false" property to the radbutton, and changed the javascript function to use "sender, args" parameters, the issues was resolved.
As for the RadTabStrip pushing the buttons down in the page when opening new windows, I have decided to have the TabStrip be horizontal at the top of the page.
Sincerely,
Keith Jackson