Thanks for the response.
I understand how this should work if I was using an iFrame, but since I'm using a frameset the only thing that returns with a window.parent.document call is my other frame (going with this example, window.parent.document.getElementByID can find Page A's frame, but not an element within page A itself). I've tried working my way down to find the button within page A's updatepanel but with no luck so far. Is there a way to go from Page B to a frameset index page to Page A's updatepanel? Any help is appreciated.