The pgAdmin 4 server could not be contacted

Hi all,
I can't get to start pgAdmin4 server mode by the command
"/usr/pgadmin4/venv/bin/python3 -s /usr/pgadmin4/web/pgAdmin4.py".

I just get the error
"ModuleNotFoundError: No module named 'httpagentparser' "

ps.: module httpagentparser is installed.
I just got success if a hit the command without the option
'-s' to python3, like this:
"/usr/pgadmin4/venv/bin/python3 /usr/pgadmin4/web/pgAdmin4.py"

But the real problem is I can't start pgadmin4 in desktop mode,
because it seems the pgdamin executable uses that command line
automatically
and crash with the error:
"The pgAdmin 4 server could not be contacted"
"ModuleNotFoundError: No module named 'httpagentparser' "

Any help to solve this problem or workaround it!

Thanks in advance.
Carlos Alberto