Added a dummy hidden field for ModalPopUp in aspx page and in code behind added ModalPopup.show().
<asp:HiddenField ID="hfHidden" runat="server />
<asp:ModalPopupExtender ID="mpueResend" runat="server" TargetControlID="hfHidden" PopupControlID="pnlPopupResend"
BackgroundCssClass="modalBackGround" DropShadow="true" CancelControlID="btnCancelR" />
<asp:GridView ID="GridMultiD" runat="server" CellPadding="3" AlternatingRowStyle-BackColor="#EDF3F7" HeaderStyle-CssClass="gridbgheading" Width="100%" HeaderStyle-HorizontalAlign="Center" OnRowCommand="GridMultiD_RowCommand">
<Columns>
<asp:TemplateField HeaderText="Resend">
<ItemStyle HorizontalAlign="Center" />
<ItemTemplate>
<asp:Button ID="btnResend" runat="server" Text="Resend" CssClass="text ButtonInline" CommandName="ViewComments" />
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>
protected void GridMultiD_RowCommand(object sender, GridViewCommandEventArgs e)
{
switch (e.CommandName)
{
case "ViewComments":
mpueResend.Show();
break;
}
}
Thank You