Inventory to Xero Invocie Sync Issues

Inventory to Xero Invocie Sync Issues

Has anyone had an issue with Invoices not syncing to Xero. 
It seems to be an issue when there is VAT on a shipping cost, but I cannot be 100% as the error is vague:

"Unable to export Invoice 'INV-000053' as the account mapped with some items does not have an account code"

It has been with the helpdesk for over two weeks but no resposne!