SAP Message WM540 - Plant & is assigned to reference plant &. Assignment not possible

Diagnosis
You wish to assign a plant to an assortment. This plant has a referenceplant, however, which is already assigned to the assortment. The plantyou have entered is therefore assigned to the assortment via thereference plant.

System Response
You cannot assign the plant to the assortment.

Procedure
The plant is already assigned via the reference plant, therefore you donot need to reassign it.