I had problems getting rtorrent to start after I maxed out the hard drive and had to manually delete some torrents. It was giving me the following error whenever I attempted to start it:
rtorrent: Could not lock session directory: "/Files2/rtorrent/session/", held by "<error>".
All I had to do was delete the rtorrent.lock file from the session directory (shown above in the error).
rm -f /Files2/rtorrent/session/rtorrent.lock