Changing salesperson on AR commission plan

Question. Our Finance department is attempting to remove one of two salespersons (50/50 split on commissions) assigned to a commission plan. At the time of attempting to save the changes, the system states that unposted invoices exists and cannot save the changes. What is the best approach to handling this situation? There are open invoices that have not been pulled into a batch and no unposted AR batches for the customer exist. As part of our customer base, we are constantly creating invoices against sales order shipments on a daily basis and rarely are there no open invoices in the system. Any guidance is greatly  appreciated.

Danny