This error occurs when an asynchronous postback occurrs after the webpage has been inactive for 90 seconds. This happens because the default value for AsyncPostBackTimeOut attribute of ScriptManager is 90 seconds. Increase this value to resolve the issue.
Eg.
< id="ScriptManager1" runat="server" asyncpostbacktimeout="800">
How does one do that ?
< id="ScriptManager1" runat="server" asyncpostbacktimeout="800">
please explain to someone who knows little about computers
sasweetie_67@yahoo.om