Archive failed (TypeError: %d format: a number is required, not NoneType in restart_position_iterator)

[Anthony O.]

When saving my files, I've got that error :

Traceback (most recent call last):
  File "/usr/bin/duplicity", line 1241, in <module>
    with_tempdir(main)
  File "/usr/bin/duplicity", line 1234, in with_tempdir
    fn()
  File "/usr/bin/duplicity", line 1207, in main
    full_backup(col_stats)
  File "/usr/bin/duplicity", line 416, in full_backup
    globals.backend)
  File "/usr/bin/duplicity", line 262, in write_multivol
    restart_position_iterator(tarblock_iter)
  File "/usr/bin/duplicity", line 192, in restart_position_iterator
    ("/".join(last_index), last_block, "/".join(tarblock_iter.previous_index)),
TypeError: %d format: a number is required, not NoneType

I'm using deja-dup (14.0.3-0ubuntu1).

Duplicity version : 0.6.08b-0ubuntu2
Python version : 2.6.5-0ubuntu1
OS Distro and version : Ubuntu 10.04.4 LTS (Linux myhost 2.6.32-41-generic #91-Ubuntu SMP Wed Jun 13 11:43:55 UTC 2012 x86_64 GNU/Linux)