You might also try disallowing the kernel from locking the cdrom. Sometimes a rogue process will hold onto the drive for no real reason. This way is often much cleaner than killing the process.
# Temporarily unlock the cdrom
echo 0 > /proc/sys/dev/cdrom/lock
# Permanently unlock the cdrom
echo “sys.dev.cdrom.lock=0″ >> /etc/sysctl.conf
via Linux CD / DVD Locked and Drive Is Not Opening / Ejecting CD.