Thanks again, I think I did do a backup with that utility, but thought I'd lost it when the update failed and the box hung. This positioner problem is a real pain though.
The problem was that I'd attempted an update rather than a new install; I just went through the official "install new image" process (I feared that would be impossible but it was very straightforward) and it's now back up, but I'm having to reinstall and scan every satellite and I'm struggling to get my V-box, which has all the positions stored, to align itself properly with the Dreambox. It's proving very unreliable at recalling the position when i want to move to another satellite.