Hi,
steps I would take:
1. Determine what kind of product categories your company is using -> UNSPSC at deepest level for example?
2. If yes: check the org model for the allowed categories for the user you are testing with
3. Ask vendor A tech team if there ever was a list sent to them
4. check the catalog transfer badi for any coding regarding product categories
5. search for the documentation regarding the implemented catalog process at your company
From your error message it looks like it is an UNSPSC code (Ceramic Beads 
) -> http://www.unspsc.org/search-code.
Robin