I got this error today. I have two max level artists painting all over the place, and a nectar maker who is selling all nectars of great quality or less.
I trotted him over for his weekly consignment sale, nothing happened. The Buy just kept disappearing from the queue. So I switched to my founder, she had the same issue.
I saved game, logged to main menu, then read where someone had said to cancel consignments. So I trotted my founder back over...she can't buy, and there's nothing to cancel now.
I guess I can either start decorating walls, or just selling them from inventory now...