When I Put Button In Updatepanel When User Click The Button Button Is Hiding Issue

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C#

ASP.NET

Javascript

CSS

Ajax

hii friends,
i am using ajax timer control.when i put timer control and button in update panel,when user click the button the button is hiding.

i am using this aspx code

<asp:UpdatePanel ID="UpdatePanel11" runat="server" UpdateMode=Conditional>
       <ContentTemplate>
                           <asp:Timer ID="Timer1" runat="server" Interval="100" Enabled="false" ontick="Timer1_Tick"></asp:Timer>

                          <table id="AllGrids" style="width: 1000px" align="center" runat="server">
                          <tr style="width: 100%">
                         <td style="width: 70%"><asp:Label ID="lblConpanyName" runat="server" Text="Label" CssClass="textbold" Font-Bold="True"></asp:Label></td>
                         <td style="width: 30%; text-align:right;">


                         <asp:ImageButton ID="BtnDownLoad" runat="server" Height="32px"
                           ImageUrl="~/img/download.png"  onclick="BtnDownLoad_Click" OnClientClick="showPopup()"/>


                           </td>
                           </tr>
                           </table>
                            </ContentTemplate>
                         </asp:UpdatePanel>

please share any idea to me.