Problem with torrent-downloading, dont start!?

I have a problem with my Transmission (torrent-downloading), it dont start to download any file. My friends has tried the same torrents-file and with no problems. I havnt had this problem before, it just started recently. I have tried BitTorrent to check if its something was wrong with Transmission but it didnt start either to download (BitTorrent say, "Checking for firewall..").

So have I change some preferences in Mac OS X or somewhere else that make this problems with torrens-download?