^^
Ok do as i say:
1. Stop the torrent from bittorrent. (pause it and not stop it)
2. Install and run azereus.
3. File --> open torrent, now select the partial downloaded file (50%).
4. Azereus will check for existing data, and will continue from 50% if all the 50% packets had been saved in your HDD. Even if starts from 45-47% dont worry.
5. Now the torrent will work properly and u will able to finish the torrent.
6. Remember to seed after you finish the download.
Did u try
BitTornado 0.3.10 ? It's very simple and a good client