Error - 'Unable to create purchase invoices. The Invoice number has already been used'

This issue occurs when trying to submit an expense with a reference that has already been used.

Check the supplier record to see if the reference has already been used. If so, amend the reference within the download expense screen to one that hasn't been used yet.

To do this:

Click on the expense
Select Edit Header Information
Change the reference
Click Save

Error - 'The Invoice has already been printed' when posting from Sales Order Batch

Create a Purchase Order that will then be delivered and invoiced to the Purchase Ledger

Use corrections to amend an invoice

Error - 'Invoice x has had detail entered and cannot be deleted'

Error - 'The invoice has been cancelled, so cannot be matched.' when matching invoice to PO