DHCP not working on network other than 192.168.1.x

[smartkid]

Host: Window 7 on a notebook
VirtualBox network: Bridged adapter
Client OS: Ubuntu Server 10.4
/etc/network/interfaces:

Code: Select all

auto lo
iface lo inet loopback
auto eth0
iface eth0 inet dhcp

The DHCP at office not working but every thing is OK at home.
The office network is 192.168.21.x, with the DHCP server 192.168.21.1
The home network is 192.168.21.x, with the DHCP server 192.168.1.1.

Any ideas ?
thanks