Webmin tries to configure the DHCP server that exists on Ubuntu 10.04 (dhcp3) but since then a new version of DHCP (isc-dhcp-server) has been used by ubuntu.
So all the initial parameters are wrong and the service cannot be started at all. In order to fix it i changed the following
DHCP server config file : /etc/dhcp/dhcp/conf
DHCP server executable /usr/sbin/dhcpd
and the 4 next options to the radio button
Please fix it and advice on how to properly configure the 4 options i put on the radio button selection.
Doing that started ok