Need some Help with Update Panel

You should use ControlValueTrigger when you try to update the content depend on a property value of another control.
Ex :
Suppose there are two update panel :
First fill with gridview, second fill with a formview to display its detail.
Then you want to refresh the content of formview based on selectedvalue of gridview. Then you should put ControlValueTrigger in second update panel.

Hope this helps.