try searching for tg3 in the logs or 'dmesg | grep -i tg3' or 'eth0' 'eth1' ... basically make sure the nic is being recognized....
Its possible that the driver is outdated for your card thus giving the error because no nic was loaded...
Another problem could be since you swapped nic's it changed the eth0/eth1/eth2 numbering and dhcp-server is set to listen on eth0 (or 1) and the new nic you added enumerated as eth2 or something...
check the 'ifconfig' command ... and see what nic the dhcp-server is listening on