We are using Moodle 1.7 and are experiencing a similar problem---the Scales page takes a very long time to appear, and when it does, it only displays a button to add a new scale. Teachers cannot edit or delete their custom scales (because they do not appear on the Scales page). Teachers are, however, able to select and use their custom scales for assignments.
We have been unable to track down the cause of this problem, so any assistance would be very much appreciated. 