Sorry, been away for a while. Brake calliper is now fixed and I've tried some of the suggestions, including new and old map map discs. In the end a reinstall of the V32 firmware (from a different source) seems to have done the trick.
However I have not been able to take it on a reasonable trip, that will be happening on Friday this week. So I'll reserve final judgement until then.
In the mean time the system is OK, unlikely to be stolen from my car and gets me to where I want to go, mostly.
If the solution had been a £400 replacement unit I don't think I would have bothered.
Andi.