IPAC error codes with no switches?

[Paladin]

I just got back from trying to fix a cocktail cab that I made and sold locally in 2004.  It has an IPAC2 connected via PS/2.  It's been working fine, but now gives 2 quick flashes followed by 12.  According to the Ultimarc website, it's a bad P2 SW4.  This particular machine doesn't use that switch.  Each player has a 4 way stick and 1 fire button.  There is also a coin slot, P1 and P2 start.

I verified the wiring by using a multimeter on the IPAC, one lead on GND and the other on each input - everything checked out fine.  I then unplugged all wires from the IPAC so the only thing connected was the PS/2, but still get the same error flashes.  There's no indication of blown components on the board.  As a last resort I removed and reseated the main chip on the board, but still get the same codes.

I'm having the guy who owns the cab email Andy at Ultimarc, but I thought I'd post here and ask if anyone has seen similar behaviour before. 

Thanks!