<cc1:ModalPopupExtender ID="ModalPopupExtender1" BehaviorID="mpe" runat="server"
    PopupControlID="pnlPopup" TargetControlID="lnkDummy" BackgroundCssClass="modalBackground">
</cc1:ModalPopupExtender>
 <asp:Panel ID="pnlPopup" runat="server" CssClass="modalPopup" Style="display: none">    
    <div class="body">
        
     <asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1" AutoGenerateColumns="true" AutoGenerateEditButton="true" AutoGenerateDeleteButton="true" >
       
        <asp:Button ID="btnHide" runat="server" Text="Hide Modal Popup" OnClientClick="return HideModalPopup()" />
    </div>
</asp:Panel>