update progress for ajax modal popup called from server side

Im trying to call ajax modal pop up from  code behide file in c#. my modal popup contain  a message and two buttons Yes /no . and have to execute some function inside the yes button in server side. I wnt to use update progress while system executing the server side function of yes button click event. How to do that.... 

I already have a update progress along with page that will dispaly for all control in this page. but when i used the below pannel4 associated with modal popup..   its events ( yes button click) not displaying any updates..

<asp:Button ID="Button5" runat="server" Text="Button" CausesValidation="False" Style="display: none" />

<!-- ModalPopupExtender -->
<cc1:ModalPopupExtender ID="mp1" runat="server" PopupControlID="Panel4" TargetControlID="Button5"
CancelControlID="btnmsgCancel" BackgroundCssClass="modalBackground">
</cc1:ModalPopupExtender>

<asp:Panel ID="Panel4" runat="server" CssClass="modalPopup2" align="center" >
<table style ="width: 100% ; height :100%;">
<tr>
<td colspan = "3" align ="center" style =" height :60%;">
<asp:Label ID="lblmsg" runat="server" Text=""></asp:Label>
</td>
</tr>
<tr>
<td colspan= "3" style =" width:2px;">
<hr/>
</td>
</tr>
<tr>
<td align ="right">
<asp:Button ID="btnmsgOk" runat="server" CssClass="btn" Width="60px" Text="Ok" OnClick ="btnmsgOk_Click"/>
</td>
<td style =" width :50px;">
</td>
<td align ="left">
<asp:Button ID="btnmsgCancel" runat="server" CssClass="btn" Width="60px" Text="Cancel" />
</td>
</tr>
</table>
</asp:Panel>

protected void btnmsgOk_Click(object sender, EventArgs e)

{

// some functions here

//while executingg themm update progress has to work..

}