Booting via iSCSI to Debian7 on HP Server BL495c G5

[Axel.Walsleben]

16x BL495c G5 Blade Servers have to boot with iPXE from different iSCSI Targets. The Servers differ only in Hardware setup They all have the same Bios and the same NIC Bootrom.
i used this setup: http://backreference.org/2013/11/24/pxe-...-and-ipxe/

The Image on all Servers is the same, it was installed on Machine 1 and then cloned.
Server 1,2,5,6,9,10 are booting as suggested, all others fail.
The failing ones make the errors 'Connection timed out.' 0x4c852035
'no more Network devices'

Sometimes i get an Red Screen with the Error Illegal OpCode.

this is the part of my php code that configures the boot process:
case '00:17:a4:77:00:32':
echo "set initiator-iqn iqn.box.fritz.client:client\n";
echo "sanboot iscsi:192.168.0.1:6:3260:0:iqn.box.fritz:storage.13\n";
break;

Thanks you all Ideas.