The error message FBA_INBOUND_CARTON_026 tells you that a specific MSKU either is not present in your Seller Central Working Shipment (which can happen if you edited or deleted quantities directly in Seller Central) or has the wrong quantity compared to Seller Central.
To resolve this, make sure the quantities of your items in Seller Central match the quantities of the items you have assigned in InventoryLab by Editing your Box Contents and sending the updated information to Amazon. We have linked some instructions if you need them :)
If you receive a list of Carton 026 errors after receiving an error for a missing expiration date, updating the required expiration date and then re-sending the Box Contents information (as seen here) should resolve the Carton 026 errors as well!
*Note: You would assign a quantity of 0 in Inventorylab if you have deleted the item from your shipment completely in Seller Central as outlined here.