Initially you have made the button visible=false and then later I assume, you have made it visible=true. Problem is although it is now updated through update panel but Javascript may fail to find it.
Try setting visibility false through CSS like
<asp:button id="btnlaunch" runat="server" cssclass="btn_def marr_5 flt_left" style="display:none;" onclick="btnlaunch_Click" onclientclick="javascript:disableRequestbtn();" xmlns:asp="#unknown" />
Hope, that helps :)