Thanks to all who replied, the problem has been solved. It was a miswired data bus. Live and learn. Now I'm having problems getting that PROG function to work-- I'm using a DS NVRAM instead of an EEPROM (but I don't think there's a difference...) it seems to be wired correctly but I still get an ERROR: PROGRAMMING.

I'll check the wiring again... but my logic probe indicates everything that should be toggling is.

Hmmm...