Configurator add-on and ImportError: cannot import name 'namedtuple'

Hello,
I installed Hass.io on a Raspberry Pi Model B+ v1.2.

The installation is successful: I can enter the home assistant main page (on port 8123).
Following the tutorial, I installed the Configurator add-on.

The problem is that when I try to start the Configurator add-on, it seems to start since no error is showns in the “Log” panel, but if I click on the “OPEN WEB UI” link, a new tab opens (on port 3218) but the browser (Google Chrome) fails to open the page (ERR_CONNECTION_REFUSED).

If I go back to the “Log” panel, I get the following error:

Traceback (most recent call last):
  File "/configurator.py", line 10, in <module>
    import json
  File "/usr/local/lib/python3.6/json/__init__.py", line 106, in <module>
    from .decoder import JSONDecoder, JSONDecodeError
  File "/usr/local/lib/python3.6/json/decoder.py", line 3, in <module>
    import re
  File "/usr/local/lib/python3.6/re.py", line 122, in <module>
    import enum
  File "/usr/local/lib/python3.6/enum.py", line 2, in <module>
    from types import MappingProxyType, DynamicClassAttribute
  File "/usr/local/lib/python3.6/types.py", line 171, in <module>
    import functools as _functools
  File "/usr/local/lib/python3.6/functools.py", line 21, in <module>
    from collections import namedtuple
ImportError: cannot import name 'namedtuple'

I googled to find a solution, it seemd to be a python issue, but I did not find any solution to fix the problem and let me access the Configurator WEB UI.

I solved reinstalling all from scratch. Maybe, it was caused by a bad installation.

Regards,
Vincenzo