SAP Message WM456 - Material & only listed as component in assortment &

Diagnosis
A material can only be ordered if it has been listed as a singlematerial or as both a single material and a component of a structuredmaterial.
If you want to order a material that has only been listed as acomponent, you have to order the whole structured material.

System Response
The system will reject this purchase order.

Procedure
Order the whole structured material.