I had about a dozen torrents seeding, and then over the last day every one eventually stopped seeding and showed ""No connection could be made because the target machine actively refused it" as tracker status in my client (uTorrent 3.2.3 under Windows XP). I read this, and many other, help threads, checked my hosts file (everything was fine), looked into resetting my passkey, etc., etc., etc.
Then, I decided to just close my uTorrent client and then restart it. Now everything is fine. So, if you have this problem, try the simple stuff first. I need to remember that myself…