I have not tried to reformat back to FAT 32, but will give this a go. I should have made it clearer that I tried two sticks, both FAT 32, both produced the same result. I only reformatted one, the other still FAT 32. Both work in my XP machine and both worked in Vista and still do on a colleague's Vista machine.
I'll try making a copy of the minidump, and updating the motherboard/chipset drivers
Thanks for the advice. I'll report back on both.