C# - ASP.NET Button click event not working
During debugging, check the CausesValidation property of your button. For some reason, one of my pages had a button defaulting to "True." When I explicitly set it to "False" everything worked.
I know that this should be resolved by now, but just to share - I just had a similar issue. In my case, the problem was that I had a RequiredFieldValidator in a page, that wasn't visible because it was part of a popup. That validator was supposed to be invoked only when clicking its related "Save" button, but since I didn't have any ValidationGroup set, it would prevent the page to submit for any clicked button. Adding a ValidationGroup to the right button resolved the issue.
Experienced the same issue recently - cause was eventually determined to be that the button was disabled by a juavascript method onbeforesubmit (designed to prevent multiple submissions), and unfortunately web forms appears to check the enabled state of the button before it allows the codebehind event to trigger.