oh .. did you try redownloading the torrent file? Something that sometimes happens is the original Tracker URL ID code gets changed. I know how to change this in Vuse, do not have a clue how you would change it in LW. Perhaps opening a new copy of the torrent file might fix it.

For Vuse, you open the freshly downloaded torrent file. Then Right-click it, choose Advanced -> Tracker/Torrent -> Edit Tracker URL(s), then Right-click on he URL in the list & choose Edit & copy the new URL. Edit the old torrent but paste in the new URL. I achieve this by opening the torrent file on windows & copy the details across to my mac (same computer) or to Transmission (another torrent program.)