I had a 750 run program written in rslogix 500 for a micrologix 1500.
there were 18 latch bits of b13:2/3 and 24 unlatches for that bit through out the entire program with 8 subroutines. add to that there were 12 error conditions that would set the bit.
when the program faulted, that bit was latched...
What I would do is set 18 different latch bits, then XIC all 18 to OTE one bit that would trip the fault condition. Then you can tell which of the 18 latch conditions was true.