I recently upgraded to Ubuntu 14.10 (from 14.04) so it upgraded Shotwell from 18.x to 20.2, and now I see this same problem (corrupted double-linked list error message) while trying to upload to Flickr. Usually before the upload actually starts (sometimes when I hit Cancel so not even starting to upload).
So far it worked after restarting shotwell from scratch so it looks like a sporadic (but frequent) bug.
I recently upgraded to Ubuntu 14.10 (from 14.04) so it upgraded Shotwell from 18.x to 20.2, and now I see this same problem (corrupted double-linked list error message) while trying to upload to Flickr. Usually before the upload actually starts (sometimes when I hit Cancel so not even starting to upload).
So far it worked after restarting shotwell from scratch so it looks like a sporadic (but frequent) bug.