Comment 74 for bug 969359

I did not have this issue until today, which I think resulted from an upgrade to gnome-settings-daemon. This morning, apt-get pulled in, among other things, a new version of g-s-d:

gnome-settings-daemon:
  Installed: 3.4.2-0ubuntu0.1
  Candidate: 3.4.2-0ubuntu0.1
  Version table:
 *** 3.4.2-0ubuntu0.1 0
        500 http://mirrors.rit.edu/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     3.4.1-0ubuntu1 0
        500 http://mirrors.rit.edu/ubuntu/ precise/main amd64 Packages

However, I have not logged out since the update, and upon returning to a screensaver state, I found the bug as described above. Restarting g-s-d seems to have made the problem go away, for now. I postulate from my experience that some occurrences might result from an upgraded g-s-d not being restarted and therefore an old binary (still running) that is attempting to use new data files?