I'm still getting occasional crashes with my ACA620, it's not as bad as some have stated here but after doing more testing this evening I'm yet to see a crash with Maprom disabled so maybe this is a factor?
Those having trouble try disabling Maprom and report back. If you had it enabled you will need to power down otherwise it stays activated on soft reset.
Spoke too soon, crashed again with illegal instruction!
I give up, it seems totally random!