This suggests that you had a system crash whilst in that return or set of accounts.

You will need to browse to where the data files for Absolute are held on your system, if you are unsure of this location you can see it through Tools / User Setup / Paths.

If you, through file explorer, browse to that location you will have a folder called Clients. Within this you will see a file called locks.map, this file needs to be deleted and this will unlock the record.