I have had an issue with iChat ever since I got my MacBook Air last year. I usually don’t bother going on forums to ask for answers as I end up figuring it out for myself. But I was stumped. I endedup on the Apple forums. It wasn’t much help.
Today, on my new 27-inch iMac, I encountered the same exact issue. I finally figured out the fix.
Previously, as seen in that forum thread, the advice was to run the Auto Accept Applescript upon receiving a message. Then I realized that the sound that was corresponding with the event was not the same. It turns out that my issue was that I was running the script on the wrong event. Instead, I should be running it on Text Invitations.
That solved all of my problems. At first glance, it seemed counter-intuitive: you are receiving a message, not an invitation. But technically, the initial message is an invitation. And thusly, you must accept the invitation first.