Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 489, in on_combobox_server_changed
    self.backend.ChangeMainDownloadServer(uri)
  File "/usr/lib/python2.7/dist-packages/dbus/proxies.py", line 143, in __call__
    **keywords)
  File "/usr/lib/python2.7/dist-packages/dbus/connection.py", line 630, in call_blocking
    message, timeout)
DBusException: com.ubuntu.SoftwareProperties.PermissionDeniedByPolicy: com.ubuntu.softwareproperties.applychanges