Interestingly (and I know this is another familiar symptom I've seen other have), if you hold down the eject button it will boot and work OK. But as soon as you let go it reboots again.

The reason that I don't think it's related to the quality of the CD/DVD disc itself is that if I can completely eject the disc (if it's reluctanct, keep pressing) then I *should* get the system to boot to menu and the GPS should ask me to insert the map disc. However, it behaves exactly the same way - ie. constant reboot cycle, but holding down the eject button allows it to boot.

I'm wondering if this is a loose connection of some kind. After some fiddling with the connections it's now on again. But I suspect it will fail again soon enough.

I would love to get a definitive problem/solution to this one as I'm sure many others would. Clearly, it's possible to have issues with a poorly burned backup disc, but I don't think that's necessarily the case here.