UPC for the listing was assigned to multiple ASINs. When you send the shipment, the ASINs conflict in the back end and cause errors in the system. This can happen when an item that used to be stickerless now requires a label. That’s because the UPC associated with this ASIN used to be associated with that ASIN only, but is now associated with more than one ASIN.
Solution: You may have to create a new listing on Seller Central.
You can first create a dummy shipment on Seller Central with this sku as its possible that amazon will change over the requirements.