Extlinux boot mistake

Another question recommented I make use of extlinux. It presents the instead purposeless message "Boot mistake". Why would not it function? Just how can I debug the trouble?

Disk format : on/ dev/sda rEFIt is mounted./ dev/sda4 is/ and also there is no different/ boot dividing.

Method of installment:

extlinux /boot

extlinux.cfg

DEFAULT Gentoo
LABEL Gentoo
  KERNEL /boot/kernel
  APPEND -