When trying to access a page that the user has no permission to, different error messages are displayed in different cases:

1. If you try to open the setup.php with a non-super admin user an "Configuration file error: No permissions to referred object or it does not exist!" error is displayed. See 1. screenshot.
2. If you try to open a configuration or administration page, for instance, hosts.php with a plain user, it displayed a "ERROR: No permissions to referred object or it does not exist!". See 2. screenshot.
3. If you try to open a page with a guest user when guest access is disabled, it shows an error with a half-rendered frontend layout. See 3. screenshot.

Instead it should always display this error:

You are not logged in.

You must login to view this page.
If you think this message is wrong, please consult your administrators about getting the necessary permissions.

If guest access is enabled, the frontend menu should be rendered as on screenshot 4., otherwise the message should be displayed on a gray background as on screenshot 5.