Transmission

Qt does /almost/ the same thing. Instead of throwing an error on clicking "OK", it closes the dialog without making the torrent. I suspect it's just a different reaction to the problem in the backend.
I can't find and nightlies or betas post-2.31 for Ubuntu, so I should file an error report, right?

Back to the problem described, usually when the tracker is rejected (while creating a new .torrent file) there is a well known problem, like using udp:// tracker URL with versions before 2.30, or a syntax error, but your example doesn't have anything obviously wrong... so don't expect an answer ...

No, I'm not doing it that way...how does one upload a torrent to a tracker other than through a torrent client?

I searched the forums and couldn't find an answer to this one. Forgive me if I didn't look hard enough.
Running Transmission 2.13 on Ubuntu 11.04 (Natty).
Downloading works well, but when I attempt to create a torrent, Transmission seems to reject /every/ tracker I throw at it, saying 'Error ...