This is a form of data corruption in that this data has reappeared from a closed year and now you are in a no win situation because Sage will not allow you to edit anything in closed years and you can't post this invoice because that original transaction actually exists in those prior years, which is why you are getting the message of the duplicate invoice number. As a work-around, you could rename that Vendor ID with a prefix of ZZZ and then run the AP aging report excluding that ZZZ Vendor ID, Save the report and just run that report all the time. If Sage support can't get that fixed, then you would need to have our data repair service fix it which we would charge for that service.