Transmission has stopped working on Ubuntu 15.04. It doesn't download anything. Check the attached pictures. I am not sure how to debug this. Pls help.
I installed Vuze and its able to download the torrents. Works fine. But I prefer to use Transmission as its very lightweight.
From the pictures it looks like something is blocking your connection to the tracker, which is what connects you to everyone else that is seeding/sharing the ISO file. Depending on where you are and what ISP you have P2P stuff like torrenting might be blocked (or illegal, even though this is a legitimate usage). I would say check your network settings and make sure nothing is set to filter out P2P (Peer-to-Peer), connections. Specifically any kind of proxy server your connection might be using, like if you're doing this at work for example.
From what I can tell from what you posted, it looks like transmission isn't connecting to peers for some reason, even though it knows about them. Since you say that Vuze works, you should probably verify that you didn't change any settings for the torrent by accident (under options, check whether a rate or peer limit is set for the torrent). Similarly, you'll want to check the global settings.
Normally I'd also suggest to check that there are no other torrents eating up all the bandwidth or connections, but your screenshot shows only one torrent active, so that's probably not it. However, did you try to get another torrent with transmission?