Check your Firewall and or router.
The Firewall (If ON) works on the basis that you can call out but the incomming stuff gets Blocked if an App is NOT allowed.
The same can be true of the router.
If you don't specifically Open the Ports it can take the outgoing part to "open" them and accept incomiong data on the same port.
The Mac Firewall is in System Preferences > Security > Firewall
If ON you need the Options or Advanced button depending on OS version
In here you need to had "Allowed Signed Software and added iChat to the List.
In the router you may need to engage UPnP if the device has it.
If not then you need to open:-
iChat 4 and 5 Ports for iChat Service TCP Ports UDP Ports iChat over AIM 5190 5190 Bonjour 5298 5297, 5298, 5353 Jabber 5220, 5222, 5223 No ports A/V Ports No ports 5678, 16393-16402
Note this is the iChat 4 and 5 Range Add port 5060 UDP for iChat 2 and 3 and extend the group of 10 to 16384-16403 (20 ports) iChat 4 and 5 also uses an undeclared Random port to do the Screen Sharing part and works if you can and do use UPnP (Or Port Mapping Protocol) to open ports in your routing device.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.3)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously