Errors like this mean that one or more of the tax codes (Australia) or GST codes (New Zealand) don't have a linked account.
What are linked accounts?
Linked accounts make the software easy to use. By using linked accounts certain types of transactions are automatically linked to the ledger accounts you have chosen. Just as there are linked accounts for tracking your debtors and creditors, there can be linked accounts to track sales, purchases and the value of your inventory items.