I can't believe this question hasn't been asked before... How do I change the message that is displayed to the user when an async postback has timed out?  I've searched the scriptmanager documentation and tried to handle the asyncpostbackerror or whatever event (which doesn't fire on a timeout), but I can't figure out how to do it.  Any hints will be appreciated.  Thanks.

Hi,

You can add your own error handler as the following code:
function StartAsyncPostBack() {
WebService.set_timeout(2000);
WebService.RunForLongTime(0, Complete, OnError); // call a method with the signature of RunForLongTime(int);
}
function OnError(result) {// your error handler
alert("error: " + result.get_message());
}

Hope this helps.