I recently ran into an issue where I was trying to dynamically create a Panel with Buttons, Labels, ect and have it popup using the AJAX PopupControlExtender.  The problem was that whenever you would click on the Button, it wouldn't fire the click event.  The event was there, it just wouldn't execute.  Anyway, to make a long story short.. I had to change the Button's UseSubmitBehaviour to false to get it working.

i.e ( Button1.UseSubmitBehavior = false);

Hopefully, someone will find this post and save themselves some time.