Yes, I deleted the contents of the backup folder as Malte suggested, then with XP at 2013, I used the FMS Data Manager to download 2014. So at this point my backup folder contained the backup.idx file and 1 .bak file of 18.6MB.
I then went and tried to do a restore and had the same problem, the restore icon flashes for a microsecond, but no restore occurs.
(The backup files cannot be correct, usually I also have an 80MB+ .bak file of the same date, sounds to me like the FMS Data Manger isn’t really backing up the full airac…)
To manually reset XP’s airac I keep a copy of the Custom Data folder from previous versions and then just copy the contents into XP, giving me the previous version of airacs.
Ian