Thanks for your response about my post. I got the solution through this link http://www.aspdotnet-suresh.com/2011...-gridview.html.

Solution : I have created one more button(Button1) with display:none mode and i set that as targetcontrolid. And i wrote data load code in other buttton(Button2), which is not targetcontrolid. In Button2, i added modalpopupextender1.show(). Its works well to me..!!!