without seeing the code my initial thought is that the variable PackSlip is not getting set to a valid number. I have had a few issues that this error gets thrown and it has nothing to do with that line it is something else i.e. adapter not getting set correctly or variable not having valid data. If you show the code I can take another look.
If it makes you feel any better, this error also occurs on 10.2.100 with CustShip.DeleteByID