Thank you for your suggestions.  Unfortunately the rebuild and verify utility showed no errors.   I tried changing the transaction date to 20 years ahead, and change it back.  That also did not clear the error.   Other transactions are not showing any problems at all.  I have deleted and re created this item a number of times.   I post a partial payment, and the correct balance owing shows in the Pay Bills window.   I can post partial payments until only $1 is owing, and the correct outstanding amount shows in the pay bills window.  But as soon as I pay the remaining amount, suddenly the entire invoice is showing as payable again.  But only in the pay bills window, not in the vendor list or the AP summary.   There are no unapplied credits linked to the invoice.

It is very strange.