Export to excel not working inside updatepanel

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ASP.NET

trigger

I have a button that exports a gridview to excel, which is working fine outside the updatepanel..
But I want the button inside updatepanel..
I have written a trigger to solve the issue, but nothing happens when I click the button, below is the code:

<div style="text-align:right;">
                    <asp:Button ID="exclexp" runat="server" Text="Export As Excel" OnClick="exclexp_Click" />
                                 <triger>
<asp:AsyncPostBackTrigger ControlID="exclexp" EventName="Click" />
</triger>
                </div>

please help I am a begginer in asp.net

when I mouseover to the trigger its showing like:

AsyncPostBackTrigger

is not a known element