how to call the server side code is call for ajax modelpopup contrl events

hai,

i am showing ajax modal popup window in that i have 2 imgeButtons(save, clear) when in save dialog is disappear but the save_click event cod is not fired what is the problem i am use following code.

In MASTER Page:-
 function ok(sender, e)
{
    $find('ModalPopupExtenderLogin').hide();
       alert("for postBack");
    __doPostBack('btnImgSave', e);
}

inClientPage:-


<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="users.aspx.cs" Inherits="users" Title="Untitled Page" EnableEventValidation="false"  %>
<%@ Register Assembly="AjaxControlToolkit" Namespace="AjaxControlToolkit" TagPrefix="ajaxToolkit" %>



   
   
   

   
       

		ImageUrl="~/Imges/addImg.png"         style="margin-left: 0px; margin-bottom: 0px;" ToolTip="Add New User"              AlternateText="Add New User"/>
BorderColor="#E7E7FF" BorderStyle="None" BorderWidth="1px" CellPadding="3"             GridLines="Horizontal" AllowPaging="true" PageSize="10"             AutoGenerateColumns="false" DataKeyNames="UserId" Width="100%"             onrowcommand="grdUsers_RowCommand" onrowediting="grdUsers_RowEditing"              >

               TargetControlID="ImgBtnAdd"
             PopupControlID="LoginPanel"
             BackgroundCssClass="modalBackground"
             DropShadow="true"
             OkControlID="ImgBtnSave"
             OnOkScript="ok()"
             CancelControlID="imgBtnClose" />
   
     
     
               
               
                    First Name :
               
               
           
           
     
               
               
                    Last Name :
               
               
               
           
           
               
               
                    Email Id     :
               
               
           
           
               
               
                    Street        :
               
               
           
           
               
               
                    City           :
               
               
           
           
               
               
                    Zip            :
               
               
           
           
               
               
                    State         :
               
               
           
           
            Country    :
           
           
           
      <%--
   --%>  
     

	GroupName="g1" />                                     Text="InActive"  CssClass="chk" GroupName="g1"/>
	ImageUrl="~/Imges/save.png" ToolTip="Save Changes" OnClick="imgBtnSave_Click" />                     <%--onclick="imgBtnSave_Click" OnClientClick="confirm('Do You Want Save');" />--%>                 <%--                    ImageUrl="~/Imges/clear.png" ToolTip="Clear All Fields"                     OnClientClick="return clearAll()"/>--%>                                     ImageUrl="~/Imges/close.png"  ToolTip="Close" />