Ubuntu 8.10 server keeps dropping ip

[grungerokker13]

We just installed 8.10 server on a few boxes and they were working fine for a while; however, today one of our boxes started dropping its static ip. We set them all up for static ip's using the /etc/network/interfaces file. The file had them as:
"auto lo
iface lo inet loopback"

We changed them to:
"auto eth0
iface eth0 inet static
address (ip address)
netmask (subnet mask)
network (network addy)"

It worked fine for a few days then all of a sudden it just started losing its ip. ifconfig shows that eth0 has no ip, so I restart networking and the correct IP is back but then in a few minutes it will drop it again. Is it because we removed the loopback interface? We did this on 6 boxes and only one is having this problem.

Has anyone encountered this before?

[coopstah13]

did you accidentally assign this machine the same IP as another on the network?

[grungerokker13]

Nope it's just an private network that we're doing so we just used private ip's.

we used:
192.168.1.1
192.168.1.2
192.168.1.3
192.168.1.4
192.168.1.5
192.168.1.6

just for now, so that we could get everything up and running.
And every machine has a different ip.