Picard 0.16 "Scan" function isn't working in Ubuntu 12.04 ("Lookup" function works fine though, see also: https://bugs.launchpad.net/bugs/959582).
It produces errors like this:
E: 140580348659456 20:29:23 Network request error for http://ofa.musicdns.org:80/ofa/1/track/: Error downloading http://ofa.musicdns.org:80/ofa/1/track/ - server replied: Invalid "cid" (QT code 299, HTTP code 400)
Scanning & fingerprinting powered by AcoustID instead of the (default) AmpliFIND results in the similar errors.
Tested affected Picard versions: 0.16-2 (from official Ubuntu repositories) and 0.16+bzr1217~ppa6~precise1 (from MusicBrainz stable PPA).
Picard 0.16+bzr1281+53~ppa6~precise1 (from MusicBrainz daily PPA) is not affected, scanning (powered either by AcoustID or AmpliFIND) works fine.