Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/defer/__init__.py", line 473, in _inline_callbacks
    result = gen.throw(result.type, result.value, result.traceback)
  File "/usr/lib/python2.7/dist-packages/UpdateManager/backend/InstallBackendAptdaemon.py", line 52, in commit
    downgrade, defer=True)
DBusException: org.freedesktop.DBus.Error.UnknownMethod: Method "Set" with signature "sss" on interface "org.freedesktop.DBus.Properties" doesn't exist