SAP Message VL424 - & serial numbers are already maintained. Quantity cannot be changed

Diagnosis
The delivery quantity cannot be changed to a number lower than theserial numbers you have already assigned.

System Response
The system rejects the change of quantity.

Procedure
First delete the serial numbers that were not delivered, therebyadjusting the number of serial numbers to match the desired deliveryquantity. Then you can reduce the delivery quantity.