partition error in booting openbsd

[sacarde]

Hi,
   I have this yabooy.conf in my apple-mini-ppc (with installed YDLinux + 
Openbsd)

# yaboot.conf generated by anaconda
boot=/dev/hda2
init-message=Welcome to Yellow Dog Linux!\nHit  for boot options
partition=5
timeout=80
install=/usr/lib/yaboot/yaboot
delay=5
enablecdboot
enableofboot
enablenetboot
macosx=/dev/hda3
magicboot=/usr/lib/yaboot/ofboot

image=/boot/vmlinux-2.6.22-0.ydl.rc4
        label=linux
        read-only
        initrd=/boot/initrd-2.6.22-0.ydl.rc4.img
        append="rhgb quiet root=LABEL=/"

image=/bsd
        root=/dev/hda4
        label=obsd
        read-only
        partition=4


linux start OK
openbsd not start, error is: unknow or corrupt partition


can you help me?
thankyou


p.s.
I have this openbsd partition from mac-fdisk:

/dev/hda4  OpenBSD openbsd   20000000 @ 13074712  (  9.5G)  Unknown


but from linux, I mount obsd partition correctly with:

mount -t ufs -o ufstype=44bsd,ro /dev/hda4 /mnt/hda4