If this is an Apple ID ending in @mac.com, @me.com or @icloud.com and the password is over 16 characters the AIM servers (As it is a valid AIM Screen Name) cannot read the password.
This applies to all versions of iChat and Messages
If you have an iCloud issued @me.com or @icloud name then these will only work in iChat 6 or above.
Apple now have iChat 6 and the Messages app also login on to me.com which in turn allows the passwords to be seen by AIM.
As a consequence iChat 5 and earlier don't login in to me.com and then the password access is not verified. (It does not work in this an earlier versions)
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Mountain Lion 10.8.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
Couple of iPhones and an iPad
"Limit the Logs to the Bits above Binary Images." No, Seriously