[Duplicity-talk] GPG error suddenly started happening?

[Scott Hannahs]

My backups have been going along just fine.  But suddenly I had to delete a 
partial file from the backup set and now I get the following in the log.

GPG error detail: Traceback (most recent call last):
  File "/sw/bin/duplicity", line 1546, in <module>
    with_tempdir(main)
  File "/sw/bin/duplicity", line 1540, in with_tempdir
    fn()
  File "/sw/bin/duplicity", line 1391, in main
    do_backup(action)
  File "/sw/bin/duplicity", line 1522, in do_backup
    incremental_backup(sig_chain)
  File "/sw/bin/duplicity", line 671, in incremental_backup
    globals.backend)
  File "/sw/bin/duplicity", line 432, in write_multivol
    globals.volsize)
  File "/sw/lib/python2.7/site-packages/duplicity/gpg.py", line 356, in 
GPGWriteFile
    file.close()
  File "/sw/lib/python2.7/site-packages/duplicity/gpg.py", line 241, in close
    self.gpg_failed()
  File "/sw/lib/python2.7/site-packages/duplicity/gpg.py", line 226, in 
gpg_failed
    raise GPGError(msg)
GPGError: GPG Failed, see log below:
===== Begin GnuPG log =====
gpg: XXXXXXXX: skipped: Unusable public key
gpg: [stdin]: sign+encrypt failed: Unusable public key
===== End GnuPG log =====

But the key seems be good, I just extended the expiration date.
% gpg -k XXXXXXXX
gpg: Note: signatures using the MD5 algorithm are rejected
pub   1024D/XXXXXXXX 2009-08-25 [expires: 2017-10-23]
uid       [ultimate] Scott Hannahs (backup) <address@hidden>

Any ideas?
Command:
nice -n19 /sw/bin/duplicity --full-if-older-than 32D --num-retries 5 --tempdir 
/var/tmp/duplicity --volsize 250 --asynchronous-upload --encrypt-key XXXXXXXX 
--sign-key YYYYYYY --gpg-options=--default-key= XXXXXXXX --force --verbosity 
Debug --s3-unencrypted-connection --s3-use-new-style --allow-source-mismatch 
<bunch of excludes deleted> /Users/<name>/Documents 
s3://objects.dreamhost.com//ZZZZZ-backups/documents

-Scott