Originally Posted by Schoenfeld
Toni has done more tests, and it appears to be a reset issue: Different A500 models have different values for the reset-pullup. Try adding a 2k2 resistor between Vcc and Reset.
Is it possible for you to add a small delay to the startup execution of your card to allow the reset line to settle, I know I have to do much the same on some of the faster PICs I use and LCD screens sometimes? Another alternative may be to cycle the reset from the expansion port before the ACA500 starts which may give a more exact reset cycle.