I send you a mail with zip. I thought it could be a mp3 probelm, but I used this mp3 with another mp3 player, which is not using your MP3Loader class and there I get the right duration after the meta data has been loaded.
I also tried it with two other mp3´s and there the onInit event hasn´t been even dispatched, although I set the listener for it in the vars. Weird!!!