You can contra the old credit note by posting a Firm invoice, then paying the invoice and the credit note together to clear the supplier ledger. Please follow the steps below to action:
From the DPS Home Screen, select Purchase Ledger.
Select Firm Invoice.
Complete the posting screen details as appropriate, then click Add to Batch, then Post.
From the DPS Home Screen, select Purchase Ledger.
Select Pay Supplier.
Enter details into the relevant fields, and tick the Invoice as well as the Credit Note, which should net to nil.
Click Post.