I have a TabContainer with two tabs. Each tab has its own updatepanel. i added an updatepanelanimationextender on the first tab for the first tab's updatepanel, and it worked. then i added another updatepanelanimationextender on the second tab for the second tab's updatepanel but the page failed to load. can two updatepanelanimationextender co-exists in one tabcontainer?

Yes.. I tried one example..

It works fine!!! 

thank you for your reply.

I found out what's my problem. the behavior id for the two updatepanelanimationextender was the same. i changed the other one and now it's working fine.