Ajax Modal Popup - CanceltargetcontrolID not firing

Question

Hi...

My aspx design is -

<asp:Panel ID="pnlFileUpload" runat="server" Style="display: none">
               <div >
                    <br />
                    <p >Add Document</p>
                    <br />
                    <br />
                    <br />
                    <asp:FileUpload ID="fileUpload" runat="server" /><br />
                    <br />                   
                    <asp:Button ID="btnUpload" runat="server" Text="Upload" OnClick="btnUpload_Click" />
                 
                    <asp:Button ID="btnCancel" runat="server" Text="Cancel" OnClick="btnCancel_Click"    />
              </div>               
            </asp:Panel>

<span class="icon_add_small_1">
                                    <asp:ImageButton ID="imgAFM" runat="server" ImageUrl="~/Images/icon_add_small.jpg" OnClick="imgAFM_Click" />
                                    <cc1:ModalPopupExtender ID="modalAFM" runat="server" TargetControlID="LinkButton2"
                                        PopupControlID="pnlFileUpload"
                                        BackgroundCssClass="modalBackground" CancelControlID="btnCancel"/>
                                    <asp:LinkButton ID="LinkButton2" runat="server" Visible="false">LinkButton</asp:LinkButton>
                                </span>
----------
Issue -
btnCancel_Click event is not firing.

When I run the portal... and click on "Cancel" button, the event is not getting fired...

Please help me out.. .I am not able to debug the issue...