TPE
It's saying it's looking up a Ticket by ID (which should be unique) but there are two matches when there should be one. Go to your database, go to the ticket table, and run the following:
SELECT `ticket_id`, COUNT(*) FROM `ost_ticket` GROUP BY `ticket_id`;
You should see a record with the COUNT being 2 and you then need to figure out which one is errant and delete it.
Cheers.