Firewall software can be configured to restrict Internet access from your computer and access to your computer from the Internet. 

It is most probable that Aces High II is not frozen, but rather that the firewall is suspending any activity on your computer because of those restrictions.  Check your firewall configuration and verify that Aces High II (aceshigh.exe) is allowed access to the Internet at all times (so you can play online in the arenas or in free head-to-head mode), and that it is allowed server status (so you can host head-to-head games).

If your firewall software is ZoneAlarm from ZoneLabs, the popup window that usually appears to ask if Internet access is to be given is masked when you try to go to online arenas or free head-to-head games.  Aces High II appears to be frozen, but ZoneAlarm is actually waiting for your answer.  Just type "RY" to instruct ZoneAlarm to let Aces High II have Internet access at all times.  You will need to do this everytime a new version of Aces High II is installed on your computer.