problem update panel event fires twice

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Ajax

here update panel event fires twice as i clicked on button
and record inserted twice why it is happening donno

please help

<asp:UpdatePanel ID="upanelfolder" runat="server" UpdateMode="Conditional">
                         <ContentTemplate>

<asp:Label ID="Label1" runat="server" Text= <%=prod_name %>

</ContentTemplate>
                          <Triggers>
                              <asp:AsyncPostBackTrigger ControlID="btn" EventName="Click" />
                          </Triggers>
                      </asp:UpdatePanel>

<asp:Button ID="btn" runat="server" OnClick="btn_Click" Text="Add" />

code behind

Protected Sub btn_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btn.Click
     //insert query
    End Sub