Update:
Thanks to everyone for their invaluable advice and suggestions. It seems that the sd card adaptor or microSD card or perhaps the device itself may be the issue. I put another sd card in the device with exactly the same files on it and it worked. Kind of. Well, it does some times. In other words, sometimes the files, map etc are loaded from the sd card and sometimes it boots up with the oroginal map.
The next step would logically seem to be deleting all files on the internal memory of the device as previously suggested. However, I'm concerned that, if the issue is the device only sometimes reading/loading from the sd card, we may end up with effectively a device that only randomly works and that when it does it's with a very old mapset.
Thoughts/suggestions on any way to test the device's hardware and components?