I want to use ajaxcombobox selectedchanged event with autopostback false.any help would be appreciated....

Question

I am using ajaxcombobox in a popup form . When i select item from combobox ,three textboxes should be prefill in popup on selecting an item.But problem is that on selecting item its working fine but when i add new item and click on next fields my popup disapprears coz of autopostback true.I am using update panel also..But nothing working ....Please i am trapped into this help me.

Regadrs 

Prerna