SAP Message WM487 - Material category & is not currently allowed here

Diagnosis
In material maintenance you are attempting to use a listing procedurethat involves manual module assignment.
At present, however, this is only possible for single materials.

System Response
Listing is not carried out.

Procedure
Finish maintaining the material and then add it to an assortment module(module maintenance) or cancel the function or use a different listingprocedure.