I'm using transmission 1.54 on my imac g5 10.4.11. And I always get the error, tracker request failed, got HTTP status code 503 (service unavailable). But it happens on every torrent. I've tried vuze, bittorrent, and transmission and none of them work on my computer. I can't install utorrent because it requires 10.5 osx. Here's a picture of the error (note: I didn't try to download them all at one time, I just left them on there to save in case I got it to work.):

http://tinypic.com/view.php?pic=6nvvqw&s=7

Sounds like you are clicking torrents that are on private trackers where you do not have an account. Thus you can not connect.