Here's some more detail that should help in resolving:
 
This problem looks to occur only when transferring into a Location that has a negative Lot qty.
 
File LOT_BXX originally looks as follows:
 
MTLOT_CODE MTLOT_LOT MTLOT_ONHAND MTLOT_LOC
999999                AAAA              10                Y
 
To duplicate this problem, we have lot-controlled customer-consigned inventory in a Location "Y"; we do an invoice and sell inventory from our main location "X", which makes that inventory location qty go negative (this inventory DOES exist in location "Y" however). then we Post the invoice of course to take the qty negative.
 
MTLOT_CODE MTLOT_LOT MTLOT_ONHAND MTLOT_LOC
999999                AAAA               10                Y
999999                AAAA               -2                X
 
We then want to go to IN-L-M and transfer from our "customer-consigned" Location "Y" to bring our Location "X" qty back to 0; the program crashes at the point a negative inventory qty is encountered, but the LOT_BXX file gets updated as follows:
 
MTLOT_CODE MTLOT_LOT MTLOT_ONHAND MTLOT_LOC
999999                AAAA               10                Y
 
The next time IN-L-M is attempted, we get past PN "999999" and it blows up on the next PN in sequence with a negative LOT_BXX qty.
 
Hope this helps. (Please note that selling directly from Location "Y" has been considered and will not achieve the results we're looking for.)