If this is an @Mac.com or @me.com name from iCloud, did you keep the password to 16 characters of Less ?
This is an AIM Server limit.
If you are using an iCloud issued @me.com name in iChat 5 or an earlier version it will not work.
They only work in iChat 6 as this version of iChat also logs in to Me.com which then allows the AIM server to "See" the password.
After that I would be guessing in the dark due to the lack of info in your post.
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
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