This morning, I turned on the computer and Rebit started to work. Previously, it just sat there telling me it was backed up. The backup disk was empty. The same day I got version 5, I reacted by formatting that disk, My Book 3, and reinstalling Rebit. Nothing. Then yesterday I reformatted My Book again, and still nothing. Now it works. Who knows why? Maybe if you keep reformatting and waiting it will eventually kick in.
We're not there yet. It's 55% done and it look like this might take 10 hours -- about 300 GB to be baqcked up on a USB 3.0 disk. The "Rebit disk" now has content. But it looks like success to me.