Diagnosis
Recipient determination via lists has been selected for this messagetype in the distribution customer model. This works only if an ALEobject type is specified for determining the object key from the IDocfor this message type in ALE Customizing. This is not the case here.

Procedure
Maintain an ALE object type for this message type in ALE Customizingunder the menu option:
Cross-application functions -> Distribution (ALE) -> Enhancements-> Master data distr. -> Extra settings for message types
or switch off recipient determination via lists for this message typein the distribution customer model.