必须在UpdatePanel'UpdatePanel1'中的触发器上设置ControlID属性

I have this code apsx:

我有这个代码apsx：

<asp:UpdatePanel runat="server" ID="UpdatePanel1" UpdateMode="Conditional" ChildrenAsTriggers="False">
    <ContentTemplate>
    <asp:Button ID="btnUpdateTable" runat="server" Text="Actualizar" Visible="False" />
    <asp:Button ID="btnGraph" runat="server" Text="Gráfico" Visible="False" PostBackUrl="ShowGraph.aspx" />
    <asp:Button ID="btnExcel" runat="server" Text="Excel" Visible="False" />
    <asp:Timer ID="Timer1" runat="server" Interval="5000"/>

    <table cellspacing="0" cellpadding="0" border="0">
        <tr><td>
            <div style="width: 100%">

                    <asp:GridView ID="GridView1" runat="server" DataSourceID="SqlDataSource1" BorderColor="Silver"
                BorderStyle="Solid" BorderWidth="1px" CellPadding="5" CellSpacing="1" CssClass="ttc"
                ForeColor="Silver" HorizontalAlign="Left" AllowPaging="True" PageIndex="1">
                <PagerSettings LastPageImageUrl="~/Images/arrow_end.gif" PreviousPageImageUrl="~/Images/arrow_left.gif" FirstPageImageUrl="~/Images/arrow_beg.gif" Position="Top" NextPageImageUrl="~/Images/arrow_right.gif" Mode="NextPreviousFirstLast"></PagerSettings>
                <RowStyle CssClass="ttc"></RowStyle>
                <SelectedRowStyle CssClass="ttcs"></SelectedRowStyle>
                <PagerStyle CssClass="ttc"></PagerStyle>
                <HeaderStyle CssClass="thc"></HeaderStyle>
                    </asp:GridView> 
        </div>
        </td></tr>
        <tr><td>
            <asp:Panel ID="pnlLabelValues" runat="server">
        </asp:Panel>
        </td></tr>
    </table>
    </ContentTemplate>
  <Triggers>
    <asp:PostBackTrigger ControlID="btnExcel" />
    </Triggers>
</asp:UpdatePanel>
<asp:Upd