So, finally it finished again to do his "first" backup and at the end I'm getting:

DUPLICITY: INFO 11
DUPLICITY: . AsyncScheduler: esecuzione sincrona dell'attività (asincronia disabilitata)

DUPLICITY: INFO 1
DUPLICITY: . making GET request to https://one.ubuntu.com/api/file_storage/v1/~/deja-dup/tricky/duplicity-full.20140327T160646Z.vol47.difftar.gpg (attempt 1)

DUPLICITY: INFO 1
DUPLICITY: . completed request with status 404 NOT FOUND

DUPLICITY: INFO 1
DUPLICITY: . making PUT request to https://one.ubuntu.com/api/file_storage/v1/~/deja-dup/tricky/duplicity-full.20140327T160646Z.vol47.difftar.gpg (attempt 1)

DUPLICITY: INFO 1
DUPLICITY: . completed request with status 200 OK

DUPLICITY: INFO 1
DUPLICITY: . uploading file duplicity-full.20140327T160646Z.vol47.difftar.gpg to location https://files.one.ubuntu.com/content/~/deja-dup/tricky/duplicity-full.20140327T160646Z.vol47.difftar.gpg

DUPLICITY: INFO 1
DUPLICITY: . making PUT request to https://files.one.ubuntu.com/content/~/deja-dup/tricky/duplicity-full.20140327T160646Z.vol47.difftar.gpg (attempt 1)

DUPLICITY: INFO 1
DUPLICITY: . completed request with status 201 CREATED

DUPLICITY: INFO 1
DUPLICITY: . making GET request to https://one.ubuntu.com/api/file_storage/v1/~/deja-dup/tricky/duplicity-full.20140327T160646Z.vol47.difftar.gpg (attempt 1)

DUPLICITY: INFO 1
DUPLICITY: . completed request with status 200 OK

DUPLICITY: INFO 1
DUPLICITY: . Eliminazione di /tmp/duplicity-8u4Jtq-tempdir/mktemp-HKj0wZ-48

DUPLICITY: DEBUG 1
DUPLICITY: . File temporaneo /tmp/duplicity-8u4Jtq-tempdir/mktemp-HKj0wZ-48 dimenticato

DUPLICITY: INFO 13
DUPLICITY: . AsyncScheduler: attività completata con successo

DUPLICITY: INFO 2 1376444438
DUPLICITY: . Processed volume 47

DUPLICITY: DEBUG 1
DUPLICITY: . Registrazione (mktemp) del file temporaneo /tmp/duplicity-8u4Jtq-tempdir/mktemp-Xo2GUK-49

DUPLICITY: DEBUG 1
DUPLICITY: . Releasing lockfile <lockfile.LinkFileLock instance at 0x7fb62b778290>

DUPLICITY: DEBUG 1
DUPLICITY: . Rimozione del file temporaneo /tmp/duplicity-8u4Jtq-tempdir/mkstemp-jfSf2p-1 ancora ricordato

DUPLICITY: DEBUG 1
DUPLICITY: . Rimozione del file temporaneo /tmp/duplicity-8u4Jtq-tempdir/mktemp-Xo2GUK-49 ancora ricordato

DUPLICITY: WARNING 1
DUPLICITY: . Pulizia della directory temporanea /tmp/duplicity-8u4Jtq-tempdir non riuscita - probabilmente si tratta di un bug.

DUPLICITY: ERROR 30 OSError
DUPLICITY: . Traceback (most recent call last):
DUPLICITY: .   File "/usr/bin/duplicity", line 1493, in <module>
DUPLICITY: .     with_tempdir(main)
DUPLICITY: .   File "/usr/bin/duplicity", line 1487, in with_tempdir
DUPLICITY: .     fn()
DUPLICITY: .   File "/usr/bin/duplicity", line 1336, in main
DUPLICITY: .     do_backup(action)
DUPLICITY: .   File "/usr/bin/duplicity", line 1457, in do_backup
DUPLICITY: .     full_backup(col_stats)
DUPLICITY: .   File "/usr/bin/duplicity", line 542, in full_backup
DUPLICITY: .     globals.backend)
DUPLICITY: .   File "/usr/bin/duplicity", line 403, in write_multivol
DUPLICITY: .     globals.gpg_profile, globals.volsize)
DUPLICITY: .   File "/usr/lib/python2.7/dist-packages/duplicity/gpg.py", line 324, in GPGWriteFile
DUPLICITY: .     file = GPGFile(True, path.Path(filename), profile)
DUPLICITY: .   File "/usr/lib/python2.7/dist-packages/duplicity/gpg.py", line 105, in __init__
DUPLICITY: .     self.logger_fp = tempfile.TemporaryFile( dir=tempdir.default().dir() )
DUPLICITY: .   File "/usr/lib/python2.7/tempfile.py", line 493, in TemporaryFile
DUPLICITY: .     (fd, name) = _mkstemp_inner(dir, prefix, suffix, flags)
DUPLICITY: .   File "/usr/lib/python2.7/tempfile.py", line 239, in _mkstemp_inner
DUPLICITY: .     fd = _os.open(file, flags, 0600)
DUPLICITY: . OSError: [Errno 2] No such file or directory: '/tmp/duplicity-8u4Jtq-tempdir/tmpRQiHUO'
DUPLICITY: .