Help booting a thin client

[d.davolio at mastertraining.it]

I have a bunch of Acer Extensa with SiS Ethernet card. And I have a boot 
problem.
I'm running Edubuntu 12.04LTS. Many others Thin Clients boot fine but 
this model is driving me crazy.
The thin client stops at "Begin: Mounting file system...Begin: Runing 
/scripts/local-top...Begin: setting up 
nbd-client...Negotiation:..size=280MB...bs=1024..sz=2293883904".
If I understand this is where the temporary root file system swap to the 
ndb root file system.

Question is, should I change the nbd-client parameters? But where?
I really need help because it's just 10 days that I'm playing with ltsp.
Thanks!
Davo