Refund from AR to AP - "invalid bank account"

Hi

When processing a refund to a customer from AR via AP, we have come up with situations where the AP system puts a hold on the payment due to an invalid bank account.

1. We have checked and double-checked that the bank account number entered against the customer standard are correct before we submit a refund request.  We have checked the bank account number against a bank account checker and we have a second person check the data entry for any errors.
2. The refund request has been submitted by AR, an invoice created in AP and approved by the Approver.