Message SAP WU056 - Plant & does not exist

Diagnosis
The plant of the plant group is not created in the plant table.
Since the plant groups are formed using customer master data, itmight be that in the customer master record the wrong referencenumber is in the plant master data or the plant master has not beencreated yet.
It might also be that it is an actual customer and not a plant.

Procedure
Check the master data.