Right, I've got past that now by adding in the avenard repos.
AVwizard went OK, and I setup the screen etc. Now when it starts I get a window with the title "Orbiter cannot register with the router. Please try again later". I've searched the forum and found some very old discussion on this, that said the fault was due to asterisk being disabled. On my machine asterisk is defnitely running. It might be that I've screwed up something else with my tinkering, so if it's not an easy fix I may be better to reinstall (at least I will be working with the very latest installer then as well).