[orca-list] Exception: SettingsManager._loadBackend failed

[John Frankish <john frankish outlook com>]

When I try to start orca-3.21.92 I get this

$ orca
Traceback (most recent call last):
  File "/usr/local/bin/orca", line 44, in <module>
    from orca import orca
  File "/usr/local/lib/python3.3/site-packages/orca/orca.py", line 78, in
<module>
    from . import settings_manager
  File "/usr/local/lib/python3.3/site-packages/orca/settings_manager.py",
line 568, in <module>
    _manager = SettingsManager()
  File "/usr/local/lib/python3.3/site-packages/orca/settings_manager.py",
line 111, in __init__
    raise Exception('SettingsManager._loadBackend failed.')
Exception: SettingsManager._loadBackend failed.

I believe orca uses a json backend for settings by default - if I bring up a
python3 console I can import json without errors.

I guess I'm missing something, but what?

Regards
John