Failure due to an unknown error

[DUVAL Jean-Pierre]

Description: Ubuntu 11.10
deja-dup 20.1-0ubuntu0.1
duplicity 0.6.15-0ubuntu2
deja-dup.gsettings and deja-dup.log are in attachements.

I tried to backup my local disk with Déjà Dup. The target is an ftp host.
I issued a failure due to an unknown error with this report :

Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1359, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1342, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1222, in main
    globals.archive_dir).set_values()
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 684, in set_values
    self.get_backup_chains(partials + backend_filename_list)
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 807, in get_backup_chains
    map(add_to_sets, filename_list)
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 797, in add_to_sets
    if set.add_filename(filename):
  File "/usr/lib/python2.7/dist-packages/duplicity/collections.py", line 94, in add_filename
    (self.volume_name_dict, filename)
AssertionError: ({1: 'duplicity-full.20111112T121652Z.vol1.difftar.gpg', 2: 'duplicity-full.20111112T121652Z.vol2.difftar.gpg', 3: 'duplicity-full.20111112T121652Z.vol3.difftar.gpg', 4: 'duplicity-full.20111112T121652Z.vol4.difftar.gz', 5: 'duplicity-full.20111112T121652Z.vol5.difftar.gz', 6: 'duplicity-full.20111112T121652Z.vol6.difftar.gz', 7: 'duplicity-full.20111112T121652Z.vol7.difftar.gz', 9: 'duplicity-full.20111112T121652Z.vol9.difftar.gz'}, 'duplicity-full.20111112T121652Z.vol3.difftar.gz')