When invoices are batched to Sage, they are listed as Unposted in Sage. This is so that you can verify the invoices before they are posted to the ledger. In the case of this error message, the invoices have not yet been posted and the ledger needs to be updated:
In Sage, choose the transactions to post.
Click "Update Ledger."
The word “Yes” will appear in the “Posted” column