Defcom's is the best advice for this.
It can be caused by two things on the whole.
1) the AIM servers go down or out of sync and lots of people get booted Off and are trying to reconnect and the server is busy.
2) the SSL Specific server goes down.
This requires that the SSL setting in iChat is manually reset (turned Off / Login/ Log out /Turn On)
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb( 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously