I have a master page that has a CollapsiblePanelExtender to create a menu on the left of the page layout. I then have a ModalPopupExtender control in the child page's content. Once I add this ModalPopupExtender the CollapsiblePanelExtender no longer displays properly with the GridView that is on the child's content. If I comment out the PopupExtender and still have the panels in place it works properly.
