PostBack event is not firing from checkbox control in gridview

[C# Programming]

hai friends

Can anyone pls help in finding why checkbox change event is not firing which is put inside a gridview.
Whenever I checks the checkbox the page is posting back but the event is not firing or is not called, why so?

Autopostback and runat= server etc are set..

Thanks in advance http://www.barakasoft.com/script/Forums/Images/smiley_laugh.gif

Santhosh