Diagnosis
The only material categories allowed at present are:
blank : standard material
00 : ditto
01 : generic material
02 : variant (of a generic material)
10 : sales set
11 : prepack
12 : display
20/21 : value-only material
You cannot currently add value-only materials using assortment modules,however. This can only be done using follow-on functions in listing orfunctions for listing materials individually.

Procedure
Please use an admissible material category.