How start OpenBSD using Grub2?

[aleunix]

/etc/grub.d/40_custom

#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries.  Simply type the
# menu entries you want to add after this comment.  Be careful not to change
# the 'exec tail' line above.
menuentry "OpenBSD" { 
set root=(hd1,4)
chainloader +1 
}

From Ubuntu:

# update-grub

$ sudo update-grub

Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.32-38-generic
Found initrd image: /boot/initrd.img-2.6.32-38-generic
Found linux image: /boot/vmlinuz-2.6.32-36-generic
Found initrd image: /boot/initrd.img-2.6.32-36-generic
Found linux image: /boot/vmlinuz-2.6.32-35-generic
Found initrd image: /boot/initrd.img-2.6.32-35-generic
Found Scientific Linux release 6.2 (Carbon) on /dev/sda10
done

But ater the reboot i don't see the menu from starting OpenBSD.
As you see previously during the update is never listed OpenBSD and, in effect, during the reboot that entry is never present.

I have tried even these combinations:
1)

set root=(hd1,4,a)
chainloader +1

2)

set root='(hd1,4)'
chainloader +1

3)

set root=(hd1,4)
chainloader +1
boot

but no one work! Damn!!! I tried for half day and i can't start openbsd!

The OS is on the sdb1 (for linux) and wd1 (for openbsd) and i use all the hdd.
Where i'm wrong?