If you receive an error message when trying to check out a flight that states the following message:
You just need to find and either un-check out or check in the reservation where the aircraft is checked out.
You can easily find what reservation is checked out by following these steps:
1. Go to Reservations on the left hand side of FSP.
2. In the drop down filter that is default as all statuses, change this to checked out and hit apply.
3. Look for the reservation in the aircraft that is checked out and either un-check it out or check it back in. Be aware of the time frame options at the top of the page and don't forget to check in the past, but also in the future.