This commonly happens when you are attempting to download the contents of the torrent, rather than SEED the contents of the torrent. To get around this, we recommend that you do the following:
Remove the torrent from your torrent client
Copy or move the contents of the torrent to the folder that your torrent client downloads into by default
Download the .torrent file from the site
Open the .torrent file in your torrent client.
If you have done the above correctly, your torrent client should hash check the content, then start seeding it. If you miss step 2, you will end up with the very problem you are having.
You can find additional information in the Upload Guide.