I've got a Ubuntu (latest build) box at Rackspace which is running the telephony app Asterisk. This is working fine. I cloned it and the clone's Asterisk wouldn't let any phone registrations through.
Someone suggested turning off the iptables, and lo and behold, it worked.
The iptables were cloned, why would they behave differently?
(the iptables were originally setup by someone who knew what they were doing-unlike me!, so i'd like to re-instate them but I don't know what stopped working)