You should know that some VPNs have this site's tracker blocked from certain countries so you won't be able to seed/leech while connected to that specific server's location. The problem can be easily fixed by switching to a different server, usually outside of the US. Try finding something close to your location so that your download/upload speed isn't compromised much.
In utorrent, the tracker's status should say "working" if everything's working smoothly.