HI,
The AIM Client may have failed to log you in if you are using an iCloud issued @me.com name
This is because Apple have set up iChat 6 and Messages to do a login to Me.com as well as AIM and this then allows the AIM server ot "See" the password.
Older version of iChat and the stand alone AIM for Mac app (and AIM Express) Logins cannot do this dual Login.
In Messages I did it this way.
Go to File Menu > Go to Chat room
Create a Name for the room
Hit Enter (After making sure it is Sending from the right account if you have more than one)
In the Messages main window a Chat with the name of the room Appears
Drag Buddies from your Buddy list to the Name of the Chat room
It will gain a white outline that the name you are dragging will get the green Add icon
Let go of Buddy
They will be added to the room and you get the Invite Message Dialogue box.
The Buddy Pic for the chat becomes stacked with the people involved.
At this point as I was testing as I typed I got Error messages saying the invites could not be sent.
I would estimate a couple of minutes went past (I was using other Screen Names also logging in with Messages on the same computer)
I also notice that AIM have launched a service they call Blast which seems to be some form of group chat so it may be changing.
Jabber Accounts
This sometimes needs you to "register" with the group chat server your particular Jabber server runs (if they do) this often requires a third party app that can do Service Discovery.
9:32 PM Saturday; September 8, 2012
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