Autocomplete doesn't work properly with usernames containing @ characters.
Some users seem to prefer having their email address as username. Autocomplete makes that character a %40 and when the Send button is pressed an error message appears saying that there's no such user.
If you ignore autocomplete's suggestion and carry on with the message everything works fine.
Now, I think that's something I can't fix myself since I haven't got a clue about Ajax or how it works.
