Hmmm... sounds like connection issue.
Do you have the newest version of Aces High 2? (2.08 patch 3)
Do you see any H2H rooms and just cant enter?
Are you trying to enter full rooms (8/8)?
Check your firewall settings. Does it allow AH?
If thats all clear, you can try to ping the MA and Other Arena servers. IP adresses can be found in the stickies in Tech Support Forum. Well try and go from there then.
As for not being able to host, this usually has to do with router/firewall settings. Maybe
this thread and the link Brooke provides help you with that.