In this scenario, the invoice was originally posted, but has since been adjusted.
When a posted invoice is adjusted, the post status of the invoice changes back to not yet posted.
It's possible to tell whether an invoice has been adjusted by checking to see whether the invoice record has an adjustment tab.
Once the invoice adjustment and reversals are posted, the post status will again reflect as "posted". To post a not yet posted adjustment, post from Accounts Payable.
1. From Accounts Payable > Administration page > click Post 2. Select the Filters Tab 3. Filter on the desired post date range or record 4. Select Include - None for any other records such as Credit Memos, Payments, Purchase Orders and Receipts 5. Validate and Post