what you guys talking doesnt make any sense
1.rtorrent 3.1 doesn't exist, that's ruTorrent the web interface
2. fail2ban doesn't have anything to do here
the issue itself is using outdated code/client and you just need to update your benc.php file (where the actual bencode is) and some of announce/download
depends what code you are using.
if you are not the site owner and just a simple user, the problem might be with the client/settings you are using
if you are the site owner, you need to update the above code files
~cheers~