That does not sound like anything that is based on a 68k exception, so it is
probably some firmware-internal integrity check - in which case, you will
have to analyze that firmware to find out what the exact meaning is.
Assuming this is some kind of EPROM integrity check, you might try to read
all the EPROMs with reduced supply voltage (in an EPROM reader or rigged-up
device, eg. using an arduino) - sometimes, if the bits start to
deteriorate, you can still read the original values when lowering the supply
voltage. You could then re-program EPROMs with the corrected original