[dnanian]

The problem is there's no general rule of thumb. But there are some relatively easy workarounds when you have trouble.

As I explain in the user's guide, this problem happens when we hit things to copy before we hit things to delete. Almost always, it's a problem with users who are dealing with large data sets in a single folder (movie projects, recordings, pictures) that they've renamed or moved, and we hit the "new folder(s)" before we get a chance to remove the "old folder(s)".

You can help SuperDuper! out by renaming or moving the same folder(s) on the destination -- or deleting something you've deleted.

Hope that helps.