Many Torrent Trackers block BETA or older clients.
I have Terastation Duo with Firmware 1.57, which was released on 19.07.2012.
A litte work with wireshark shows that this firmware uses a utorrent version that uses the peer_id UT300B, which identifies the Torrent client as a Utorrent 3.0 BETA.
Utorrent 3.0 Beta is about 1 or 1 1/2 years old.
I think updating to a up-to-date and stable, "non BETA", version of utorrent could be the solution to many of the "Torrents slow" and "Torrents don't download" problems