go to "Site administration/Development/Debugging" and activate "debugonlyselected". Select a user from the users box on the right side and click on "Add". The user should appear on the left side. Repeat the previous step for all users you want to see the debug messages. It could be normal users or admins. Select the debug settings below the user selector. Login as one of the selected users. Force some error messages e.g.: some senseless lines in a view.php or so. The error messages should be shown to the user. Login as admin again and remove this user from the list: Select the user on the left side and click on "Remove". Login as this user again and the error messages should disappear.