[syslinux] extlinux-4.0 can't boot on our platform.

[孤云独闲]

Hi all:
    my filesystem is btrfs. /boot and / is  on the same partition(/dev/sda2,
format btrfs).  i install syslinux as following:
     1.  rpm  -ivh syslinux-4.00-1.i386.rpm
syslinux-extlinux-4.00-1.i386.rpm syslinux-tftpboot-4.00-1.i386.rpm
     2.  extlinux-i /boot/extlinux. (the extlinux.sys can't be create on the
directory).
     3.  i copy extlinux.conf to  /boot/extlinux . (of course , i have edit
the extlinux.conf)
     4. extlinux -U  /boot/extlinux
    5.  cat /usr/share/syslinux/mbr.bin  >/dev/sda.

i reboot , but the system can't boot,  the screen show tips "No DEFAULT or
UI configuration directive found!" , i doubt mbr isn't installed.
    do you tell me why and what  i do next?

    many thanks!

-- 
Best Regards,
tomsun