Steps to reproduce:

1. login as super administrator and disable guest user
2. make a logout
3. try enter to the overview.php page by using URL

Result:
An error message "You are not logged in" will be displayed. It is correct. But PHP error also will be generated:

 - Undefined index: refresh [overview.php:40 -> require_once() -> CWebUser::getRefresh() -> CConfigFile->{closure}() in include/classes/user/CWebUser.php:249]

Same errors on other pages: latest.php, history.php, charts.php, screens.php, srv_status.php and queue.php