Diagnosis
There are a variety of different reasons:
1 = Number is used in WM itself in the future, for creating
reference numbers in the current number range.
3 = Number is used in WM itself in the future, for creating
reference numbers in a further number range.
5 = Number has already been assigned.

System Response
It is not possible to create the picking wave.

Procedure
When you choose the number ranges for delivery groups and for referencenumbers, you need to ensure that they are separate, i.e. the samenembers cannot be planned for both objects.
Please inform the person responsible for Customizing.