Webmin version is 1.441 Debian 4.0
This is a problem that affects system with more than one network card. This is what i did.
Linux firewall, then ticked activate at boot to yes, and then clicked on the button Activate at boot. This will put the following line, post-up iptables-restore < /etc/iptables.up.rules in your /etc/network/interfaces. The problem is that this line is placed imidiately after description of the first interface where it should be at the end of the interfaces file. This causes system not to start properly when rebooted. To fix the problem just move the offending line to the end of your interfaces file and reboot.