Ajax modal pop up extender

hi,

i am using Ajax modal pop up extender. in that popup i display gridview and selectAll Checkboxes button and OK and cancel buttons.

         my aim is if i click selectALL button that time all checkboxes in Gridview are selected.

         my problem is if i click selectAll button popup is not appear and again i click linkbutton that time popup is displayed with selected all checkboxes in gridview.

         i tried in breakpoint also in that case code is End no output is displayed.

please give a solution.

Thanks