An internal audit investigation involved conducting compliance tests on the processing of purchase invoices.

The purchase ledger clerk compares invoices against purchase orders and passes them for payment The invoices are then input into a computerised purchase ledger system The system checks that the supplier has a valid purchase ledger account, as authorised by the chief buyer, before crediting the supplier's account with the value of the invoice.

The internal auditor checked a sample of recorded purchase invoices against their corresponding purchase orders The internal auditor found four cases where invoices could not be agreed to corresponding purchase orders.

What is the potential significance of this compliance error?