Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler);

function EndRequestHandler(sender, args) {
	if (args.get_error() != undefined && args.get_error().httpStatusCode == '500') {
		var modalPopupBehavior = $find('programmaticModalPopupBehavior');
		modalPopupBehavior.show();
		args.set_errorHandled(true);
	}
}