If you try to log in to an AIM account via iChat that's already in use on a different computer, you may experience some login issues. Here's what can happen if you try to do this. As a general rule, you should only log in to your iChat account on one computer at a time.
Note: This document doesn't apply to Bonjour or Jabber messaging.
If you log in to iChat with an AIM account on a Mac OS X 10.4 Tiger computer and then log in with the same account on a different computer that has Mac OS X 10.4, 10.3.9, or an earlier OS installed (or via a Windows-based PC, cell phone, or PDA device), your iChat session will disconnect (log out) on the Tiger computer (you'll be connected on your second computer or device). No alert will display on either computer/device when this happens.
If you try to log in to the same AIM account using iChat on two different computers or devices with Mac OS X 10.3.9 or earlier, the following alert appears in iChat on both computers:
Your screen name (account name) is now signed into AOL(R) Instant Messenger(TM) in 2 locations. To sign off the other locations, reply to this message with the number 1.
If you reply with "1," the first computer from which you logged in to iChat will be logged off (set to offline). If you ignore the message or don't reply with "1" (and both Macs remain logged in), both computers will receive all replies to messages you send, which could cause confusion when you go back to the first computer.
This document will be updated as more information becomes available.