The torrent you are trying to add is already in the list of torrents.

[phuocrea]

I deleted a downloading torrent with the Remove button in the top bar, but then when I try to add that that torrent again it gives me the error message: The torrent you are trying to add is already in the list of torrents. Do you want to load the trackers from it?

I tried rebooting but it doesn't work still.

I found this other topic, for windows, but I can't locate the resume.dat equivalent for Mac:

https://forum.utorrent.com/viewtopic.php?id=119916

[phuocrea]

Ok, found them.

Go to:

~/Library/Application Support/uTorrent/

Delete:

resume.dat

resume.dat.old