AsyncPostBackTimeout Property needs to set which gets or sets a value that indicates the time, in seconds, before asynchronous postback time out if no response is received from the server.
<asp:scriptmanager id="scriptManager1" runat="server" asyncpostbackerrormessage="We can not serve your request at this moment.Please try later." asyncpostbacktimeout="36000"></asp:scriptmanager>
The default value of this property is 90 second. We can also set the user defined error message using asyncpostbackerrormessage property (as shown in above code) for time out.