I have solved it myself...
I have just added AsyncPostBackTimeout="3600" in ScriptManager's property and it is working. The code is given below :-
<asp:ScriptManager ID="ScriptManager1" runat="server" AsyncPostBackTimeout="3600">
</asp:ScriptManager>
It is working fine in my local machine and also in the server machine where my project hosted.
But After hosting it is not working in user's machine who is using my project through hitting my project URL. Is there any IIS setting i have to do for update panel AsyncPostBack Timeout.
I need Immediate help...
Thanks in advance...