<asp:postbacktrigger controlid="Button7" xmlns:asp="#unknown">
I think you need the eventname="click" in the trigger'
Or because the button is inside the update panel, the ID name is prefixed with something like $CT_100_button7
Try in the button
<asp:button xmlns:asp="#unknown">
ID="Button7"
ClientIDMode="Static"
runat="server"
CausesValidation="False"
onclick="Showbutton_Click"
style="z-index: 1; left: 7px; top: 123px; position: absolute"
Text="Show" />
</asp:button>
http://msdn.microsoft.com/en-us/library/system.web.ui.control.clientidmode%28v=vs.110%29.aspx[
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