it would appear that the problems with my replacement AV80R are all down to software/firmware. After much chasing around today I was asked to call Harry M Pilot shop, Edinburgh, where a helpful Danny was up to speed with the units. He sent me a link to a webpage where I have been able to obtain a download which cures the problem. Something in the early Go-Drive software objects to some towns (Reading, Birmingham,Bristol etc) and causes the unit to crash when trying to go there. It was fixed in May 09 but they are still shipping units made in 2008 with the then latest versions. Somewhere along the way there has been a "step change" in the firmware which changes the way the update procedure operates and some units need special handling to move forwards.
It would seem that I am sorted now but .................Time will tell.
Rans6Andrew