A few days ago I noticed, that Transmission in my Ubuntu 10.04 machine suddenly couldn't download anything anymore. To overcome this I have uninstalled and reinstalled Transmission and tried downloading with other clients (Deluge, Vuze) well seeded torrents (ubuntu iso images for example) without success. On the same computer I have also installed Ubuntu 10.10 and Windows 7, which I rarely use. What makes the problem I encounter weirder, is the fact that downloading via torrents works fine in my Ubuntu 10.10 and Windows partitions but not in Lucid Lynx. Browsing the web for similar problems didn't give me answers. Any help would greatly appreciated.
The problem is solved. My Peerguardian Linux installation caused all the trouble due to either some kind of a bug or some configuration adjustment I tried but can't remember. This was determined by the use of Wireshark (it informed me that the torrent clients connect to the trackers) and by getting the output of sudo iptables -L in a terminal (the output showed that pgl interfered with my machine's iptables rules). Temporarily terminating the appliance of these rules with sudo iptables -F proved the aforementioned hypothesis. Finally I uninstalled and reinstalled Peerguardian Linux and thus solved the problem.