Thank you Charlie.
Point 1 accepted. Sorry, finger trouble.
Point 2. You quite often point users at the bug tracker, but I think you forget that many users do not have your confidence to assume they are dealing with a bug.
I looked up a few forum posts about backup2 on v7 which demonstrate that there are folk using it sucessfully. In the backup2 bug tracker there are a few bugs, but none associated with show-stopping installations. My assumption in this case is that I have missed something, rather than discovered a bug.
I've had a bitch of a day trying to do this upgrade.