Ok.

Booting current grml64-small from the network fails with a kernel panic. serial
console output from a KVM VM is attached as daily.bootlog.

My ipxe config file is:
#!ipxe

kernel http://192.168.19.254/boot/vmlinuz
fetch=http://192.168.19.254/boot/grml64-small.squashfs quiet boot=live lang=us
nomce apm=power-off noprompt noeject vga=791 debug=1 serial console=ttyS0,57600n8
initrd http://192.168.19.254/boot/initrd.img
boot

The last .iso that works fine with network boot is
grml64-small_testing_20120528.iso. Starting with
grml64-small_testing_20120612.iso, the kernel panic shows itself. This includes
http://daily.grml.org/grml64-small_testing/2012-07-06_05-31-17/grml64-small_testing_20120706.iso.

Greetings
Marc