Example of error received when adding items in bulk:
20160516-B00VBI3CZK-45-Az-89.98) response: ERROR_CODE: InvalidRequestException.
ERROR_MESSAGE: Invalid Request creating FNSkuMap.
The reason for this error is that one of the SKUs in the batch being added is more than 40 characters long, Amazon doesn't allow SKUs that are that long. To bypass this error change the SKU to 39 characters or less then add the item once more.