Hi,
I had some problems with a torrent, which contained a colon ":" in its filename. When I added the torrent via the transmission web interface, I got following error message: "Error: Unable to save resume file: File exists". Looks like the torrent file could not be saved correctly. It was truncated right before the colon and so the transmission torrent could not download the files...
However, I found a workaround: I started the torrent with my uTorrent client, which saved the torrent file without the colon somehow and then I moved the file to the autoload directory of the transmission client.