HELP! booting usb-flashdisk fails

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whenever i boot from my self-created bootable
usb-stick, it fails with the following error
from boot2:

---------------------------------------------
Invalid label
Invalid label
No /boot/loader

FreeBSD/i386 boot
Default: 0:fd(0,a)/boot/kernel/kernel
Invalid Label
No /boot/kernel/kernel
---------------------------------------------

i also tried the paths
0:da(0,a)/boot/kernel/kernel
0:ad(0,a)/boot/kernel/kernel
without success.

hardware used: (FreeBSD 6.1-RELEASE):
Motherboard: GigaByte GA-8SIMLP
Flash-Disk0: Kingston Data Traveler 2.0 256MB
Flash-Disk1: Corsair Water-Resist Flash 512MB

created a bootable usb-drive using:
fdisk -BI /dev/da0
bsdlabel -w -B /dev/da0s1
newfs -m 0 -o space -n /dev/da0s1a

then i installed the base-package and the GENERIC
kernel into /dev/da0s1a, and ensured that the
kernel is really to be found at /boot/kernel/kernel.

i also tried this with the same errors:
bsdlabel -w -B /dev/da0
newfs -m 0 -o space -n /dev/da0a
(os installation the same as above)

i tried this with both usb-sticks, both of them fail.
trying them on a HP-Server works perfectly to the root-
login.

the bios supports booting from:
USB-FDD, USB-ZIP, USB-CDROM and USB-HDD.
i tried all of them. also, i set the boot-priorities
to only boot HDD-0 and removed all other drives.
obviously, no success.

btw, booting from a real hdd/cdrom works.

any really smart ideas on this?