You commited a completed BitTorrent with several files in it, but the disk was too small and the donkey could not write it to the incoming dir. Now you're stuck with a big file containing all the files from the torrent.
NB: there's a bit of confusion regarding the .torrent files. torrent links end in .torrent, are downloaded from the net, and contain infos where to get the file. However, mldonkey creates a temp file called <filename>.torrent in the incoming dir when completing a download. these two files are not to be confused with each other, or mayhem will set upon your shore ;)
o restart the bt download from the .torrent link
o kill mlnet
o open files.ini; check the file_id
o copy the completed download into the mldonkey temp dir, overwriting the file with the name BT-<file_id> (if it exists)
o files.ini: change all the zeroes in file_chunks to twos (ones seem not to work)
o start mlnet
the donkey will then verify the chunks, and commit the file.
You might consider renaming your big .torrent file before starting this procedure. I just lost my completed 2.1gb mandrake 9.2 download...