Error:

FBA_INBOUND_CARTON_016

Reason:

Your total unit count between Seller Central and Seller Champ do not match.

Resolution:

The Amazon FBA manifest is still editable and the unit count will not match unless you proceed to "Finish All" in the "Label and Pack" section.
It is only then, that the final box content will be transmitted to Amazon and the units will match. 

If You're Sending Pallets.

If you are sending pallets, then sending a box content information is not necessary.

Once the items are inside their respective boxes and on the pallet to be shipped to Amazon, the shipment will be reviewed, once it arrives at the Amazon Fulfillment Center.
The shipment is regarded as a pallet and not as boxes. If you still have not finished the order on Seller Central you can still un-select that option in the shipping section.
This should take care of the error.

Another smart thing to do is to make use of the 2D labels.
You can print it through the 'Label and Pack' section and can be applied on all the boxes on that pallet.