[dnanian]

I assume this happens when you have a scheduled backup, but the destination isn't present?

If so, the problem is that SuperDuper! is in a "no user interaction" mode due to the schedule, but when you changed the drive selection, the settings were changed. When you try to quit, we know we need to prompt you to save the settings, but we can't because we're not allowed to do so.

To work around this problem, save (Cmd-s) before you try to quit. That should take care of it.

Note, too, that our new mount/unmount feature should prevent this from happening as often to you.

Let me know if that helps!