500kg did exist physically in stock. The lot history shows the purchase received on PO1234 on 11th July wasn't completed correctly as there is no user ID on the line.
works order 1234 was receipted in twice (one without a user name and one with a user name). Why is the username missing?
If you have the Lot attributes switched on and exit the receipt screen before the record is saved, corruption can occur, resulting in missing information in random Lot records.