The error FBA_INBOUND_CARTON_027 is usually accompanied by FBA_INBOUND_CARTON_015.
It has to do with an item requiring an expiration date, but not being provided one. When that happens, the information for that box cannot be sent over to Amazon properly and the FBA_INBOUND_CARTON_027 results.
Unfortunately, Amazon does not provide to us which MSKU is the culprit in this case. If you need help determining which item requires expiration dates, Amazon has a help article around Date- and Temperature-Sensitive Products . Seller Support should also be able to give you specifics if needed, but we know contacting them is no one's idea of a good time.
Once you have found the MSKU(s) that are causing the trouble, you can alter or add the Expiration date by clicking the 3 horizontal lines to the right of the shipment under Working Shipments and selecting Box Content Information
Then, click directly on the expiration date (or N/A) and it will turn into an editable field to update
Once all of the needed changes have been made, click the Transmit Updated Boxes button in the lower right hand corner to resend your Box Content Data to Amazon.