The problem here is that an invoice with freight on it will not sync over to MYOB. The error above comes up in the error logs.
1) Go to Integrations - Accounting Integrations - MYOB Settings and take note of the account in "Freight Sales Account"
2) Log into MYOB through your AccountRight software
3) Go to Setup - Linked Accounts - Sales Accounts
4) Tick "I charge freight on sales", and select an account in this area
5) Click OK to save.