button outside of modalpop up and update panel is not firing up

Hi,

I have a button which worked perfectly fine previously code as below

  <asp:Button ID="btnAdd" runat="server" Text="Add" OnClick="btnAdd_Click"/>

After i added modal pop up and update panel inside modal pop up.  button click outside updatepanel is not working. if i take out update panel , working back again.

(clicnk inside grid view, show pop up and can update data on pop up)

 <asp:Button ID="btnShowPopup" style="display:none" runat="server" />
    <ajax:ModalPopupExtender ID="modalUpdateRole" runat="server" TargetControlID="btnShowPopup"   
                            Enabled="True"  BehaviorID="MPE" BackgroundCssClass="modalBackground" CancelControlID="btnClose"
                            PopupControlID="searchpopup">
    </ajax:ModalPopupExtender>

   <asp:UpdatePanel ID="upCustCode" runat="server">
                        <Triggers>
                            <asp:AsyncPostBackTrigger ControlID="btnUpdate" />
                        </Triggers>
                        <ContentTemplate>
                            <div id="searchpopupinnerbtn">
                                <div id="searchpopupinnerbtnleft">
                                    <div class="searchpopupinnerbtnleftinnerleft searchpopupmargindrop5">
                                          <asp:Label ID="lblS" runat="server" Text="S" CssClass="contentfont"></asp:Label>
                                    </div>
                                    <div class="searchpopupinnerbtnleftinnerright">
                                        <asp:TextBox ID="txtSU" runat="server" CssClass="contentfont" Width="170" Height="25"></asp:TextBox>
                                        <asp:ImageButton ID="btnUpdate" runat="server" Width="20" Height="20" CausesValidation="false"
                                                         ImageUrl="~/Images/buttons/update.png" onclick="btnEdit_Click"></asp:ImageButton>
                                        <asp:RequiredFieldValidator ID="rfvtxtU" runat="server" ErrorMessage="*" ControlToValidate="txtSU" CssClass="redcolor"></asp:RequiredFieldValidator>
                                    </div>
                                </div>
                             </div>
                        </ContentTemplate>
                    </asp:UpdatePanel>

Please advice