Ah, that's from an old bug. It means in the past you've transfered items to people that were still in your shop.
So yeah, you broke your shop! It can be fixed, but annoyingly I'd require the exact items that were in the shop. You could PM veb to empty your shop, that'd fix it & would be the quickest & easiest method.
(remember to ask the veb nicely, they bite if startled!)