SAP Message VL688 - Reason &1 was given more than once for item &2 (please change)

Diagnosis
You have assigned a deviation reason more than once per delivery item.

System Response
Multiple assignment of the same reason to one delivery item is notallowed.

Procedure
Change the entry so that no reasons are assigned multiple times peritem and increase the difference quantity of the reason that wasassigned more than once, if necessary.