ernel panic - not syncing: Attempted to kill init! exitcode=0x00000100

We are trying to provide Ubuntu desktop (ubuntu-14.04.1-desktop-amd64.iso) to our labs for studs, which just wanna give it a try.
Unfortunately it doesn't work: If it tries to exec the final step (e.g. run-init /root /sbin/init textonly toram </root/dev/console >/root/dev/console 2>&1) it panics:

[ 320.076015] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100
[ 320.076015]
[ 320.085145] CPU: 25 PID: 1 Comm: run-init Not tainted 3.13.0-32-generic #57-Ubuntu
[ 320.092709] Hardware name: WBS F224A-DE5/X9DRH-iF, BIOS 3.0b 04/28/2014
[ 320.099315] ffff883fce017380 ffff881fd31cde78 ffffffff8171bcb4 ffffffff81a4e5e8
[ 320.106792] ffff881fd31cdef0 ffffffff81714eb5 ffffffff00000010 ffff881fd31cdf00
[ 320.114271] ffff881fd31cdea0 ffffffff81f239e0 0000000000000100 ffff883fd2d60398
[ 320.121750] Call Trace:
[ 320.124215] [<ffffffff8171bcb4>] dump_stack+0x45/0x56
[ 320.129360] [<ffffffff81714eb5>] panic+0xc8/0x1d7
[ 320.134158] [<ffffffff8106a3a1>] do_exit+0xa41/0xa50
[ 320.139213] [<ffffffff81020d45>] ? syscall_trace_enter+0x145/0x250
[ 320.145474] [<ffffffff8106a3e7>] SyS_exit+0x17/0x20
[ 320.150442] [<ffffffff8172c87f>] tracesys+0xe1/0xe6

I've no clue, what the problem could be. Already tried to append kernel params 'selinux=0 apparmor=0 enforcig=0' but without success :(

The /root fs seems to be properly populated (overlayfs).

Any hints?
---
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
BootDmesg: (Nothing has been logged yet.)
CRDA: Error: command ['iw', 'reg', 'get'] failed with exit code 1: nl80211 not found.
CasperVersion: 1.340
DistroRelease: Ubuntu 14.04
LiveMediaBuild: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
Lsusb:
 Bus 002 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
 Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 001 Device 003: ID 0557:2221 ATEN International Co., Ltd Winbond Hermon
 Bus 001 Device 002: ID 8087:0024 Intel Corp. Integrated Rate Matching Hub
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
MachineType: WBS F224A-DE5
Package: linux (not installed)
ProcEnviron:
 TERM=linux
 PATH=(custom, no user)
ProcFB:

ProcKernelCmdLine: BOOT_IMAGE=http://141.44.24.61/boot/hostname-14.04.1-desktop-amd64/vmlinuz root=/dev/nfs netboot=nfs nfsroot=141.44.24.61:/data/mnt/hostname-14.04.1-desktop-amd64 boot=casper locale=de_DE.UTF-8 pw=$6$7CPMoOcQ$n3dtobqEnQrvJwQUKI/CoowOFI9AyUyf9I1eGY0.WK0s.PeuYpnQcVcsxt/6gN8ksJ7U2wSgAr0yavpDv4CH.0 textonly console=ttyS1,115200 debug selinux=0 apparmor=0 enforcing=0 break=init toram initrd=http://141.44.24.61/boot/hostname-14.04.1-desktop-amd64/initrd.lz BOOTIF=01-68-05-ca-0a-49-be
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
PulseList: Error: command ['pacmd', 'list'] failed with exit code 1: No PulseAudio daemon running, or not running as session daemon.
RelatedPackageVersions:
 linux-restricted-modules-3.13.0-32-generic N/A
 linux-backports-modules-3.13.0-32-generic N/A
 linux-firmware 1.127.5
RfKill:

Tags: trusty
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
Uname: Linux 3.13.0-32-generic x86_64
UpgradeStatus: No upgrade log present (probably fresh install)
UserGroups:

WifiSyslog:

_MarkForUpload: True
dmi.bios.date: 04/28/2014
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: 3.0b
dmi.board.asset.tag: 0672042101108
dmi.board.name: X9DRH-iF
dmi.board.vendor: Supermicro
dmi.board.version: 1.02
dmi.chassis.asset.tag: 0672042071494
dmi.chassis.type: 23
dmi.chassis.vendor: Supermicro
dmi.chassis.version: CSE-216BA-R920LPB
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvr3.0b:bd04/28/2014:svnWBS:pnF224A-DE5:pvr3.0:rvnSupermicro:rnX9DRH-iF:rvr1.02:cvnSupermicro:ct23:cvrCSE-216BA-R920LPB:
dmi.product.name: F224A-DE5
dmi.product.version: 3.0
dmi.sys.vendor: WBS