Hi Jono is MFMEV20.1 installed and working independently of Arcade Simulator?
Arcade Simulator by itself doesn't actually emulate the machines, it relies on MFME to provide the core emulation. when you're walking around the arcade and seeing the machines in attract mode what you're actually seeing is a kind of clever 'cheat' that the simulator does to make it look like there are a load of working machines there, when you walk up to a machine and press ENTER, that's when Arcade Simulator will try to invoke MFME to begin the actual emulation of that machine.
MAME is installed and working independently, however on closer inspection it seems it maybe version 2.0.
I have a couple of ROMS downloads already which I can play directly through MAME. When in the arcade, I can walk round and see all the machines in attract mode, the problems start when it comes to actually playing them.
After choosing a machine, I press <Enter> and it 'greys out' but then won't boot up and freezes, leaving the machine with <Esc> returns to the arcade but as I say without being able to play the machines.
Edit: Updated MAME and all working correctly now, thanks a million mate
Edit II: Just having a play around and noticed the arcade has only gone and got my favourite all time machine EVER! - Pharaoh's Gold Club !! - Although having played it just, it does seem "suped up" compared to the one I used to play in the wild.