Little update.
I've dumped the ROMs from the game board and compared them to the set in MAME (set 4, I think) and they've checked out fine. One thing I've noticed is that in the original set in MAME there are 3 .bin files which I think are the security PIC files. Can anybody confirm this?
I've read that Security ERR 41 is to do with the Stake/Prize key but I have checked this out and it is set up fine and the switches test fine on a multi-meter.
Another strange thing I've noticed, is that playing my dumps (and any other dumps) through my version of MAME makes a 'Fatal IIC 1' error come up.
So, to sum up, I've tested some things and got nowhere