Comment 7 for bug 854818

Same here, 11.10 and Gnome Shell.
Some other infos:

Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 649, in on_isv_source_toggled
    self.backend.ToggleSourceUse(str(source_entry))
  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)
dbus.exceptions.DBusException: org.freedesktop.DBus.Python.AttributeError: Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/dbus/service.py", line 702, in _message_cb
    retval = candidate_method(self, *args, **keywords)
  File "/usr/lib/python2.7/dist-packages/softwareproperties/dbus/SoftwarePropertiesDBus.py", line 156, in ToggleSourceUse
    self.toggle_source_use(source.encode("utf-8"))
  File "/usr/lib/python2.7/dist-packages/softwareproperties/SoftwareProperties.py", line 433, in toggle_source_use
    source.disabled = not source.disabled
AttributeError: 'NoneType' object has no attribute 'disabled'