hdparm as of 6.2 features the PIO data security commands that enable the user to
lock and unlock IDE drives. These functions need CONFIG_IDE_TASK_IOCTL to be
2.6.14-1.1637_FC4 has been released as an update for FC4.
Please retest with this update, as a large amount of code has been changed in
this release, which may have fixed your problem.
$ grep CONFIG_IDE_TASK_IOCTL kernel-2.6.14-i686.config
# CONFIG_IDE_TASK_IOCTL is not set
Since you haven't touched the config files this hasn't been fixed!