I finally figured it out!
On my parent web control I already had implemented a RadAjaxManager. So when I loaded up my second web control with its own RadAjaxManager, the javascript was getting confused as to which manager to use.
Enter: RadAjaxManagerProxy -> http://www.telerik.com/help/aspnet-ajax/ajax-ajaxmanagerproxy.html
After implementing this, my controls worked beautifully!
Hope this helps others, if not myself later down the road when I forget.