ftp to your PS3//dev_hdd0/home..find the account then go into the trophy's folder and look for the ghosts trophy folder(mine is NPWR04874_00)
If yours is the same back it up to your PC and then delete the folder on your PS3
Re sync with PSN.it only works if you have previously synced the ghosts trophy's with PSN before
I have had the same issue before with other games and i delete the whole trophy folder and resync an download from PSN
If that dont work Restore your PS3 File System & Database or complete wipe and restore(back up saves)