Kernel panic while booting from USB stick created with fai-cd

[Jacob Rief]

Hello,
currently I am creating a fai-image for a customized Debian squeeze
distribution, which shall be bootable from an USB stick.
I can boot this distribution through PXE. I can also create an ISO
image, burn it on CD and boot without problems. If however I put the
exact same image onto an USB stick, and I boot from there, I get a
kernel panic.
This works:
fai-cd -m /var/www/debmirror /tmp/demo.iso
then burning on CD, then booting, everything works fine.

This does not work:
fai-cd -m /var/www/debmirror -u /media/stick
then booting from USB stick, I get a kernel panic (see below).

I also tried with the ISO image for i386, (using FAI 3.4.8, kernel
2.6.32, size 563MB, http://fai-project.org/fai-cd/faicd-3.4.8.iso) and
transferred that on my USB stick as described in paragraph
"FAI CD on a USB stick (using grub2)" on page http://fai-project.org/fai-cd/
but I get the same kernel panic
(...snip...)
mount: mounting /sys on /root/sys failed: No such file or directory
mount: mounting /proc on /root/proc failed: No such file or directory
Target filesystem doesn't have requested /sbin/init.
/init: line 276: 6: Bad file descriptor
[    7.815880] Kernel panic - not syncing: Attempt to kill init!
(...snip...)

I am using fai-3.4.8 (from testing) on a fresh Debian Squeeze amd64
installation. Before I used version fai-*-3.4.7 from stable, but in
order to create a CD ISO image, a component was missing (I forgot
which one), therefore I switched to version 3.4.8.
Any ideas or hints?

Jacob