"Bit Message" in python 2.7 ?

Did someone solve "Bit Message" task with python 2.7? I have the following error raising on test 11, 10 or 9 (it changes at every run)

run_data = echo_send_recv_json(globals()['do_'+run_data['do']](run_data)), File "/opt/checkio/runners/py27.py", line 179, 
        in echo_send_recv_json, return json.loads(echo_send_recv(json.dumps(send))), File "/usr/lib/python2.7/json/__init__.py", line 231, 
        in dumps, return _default_encoder.encode(obj), File "/usr/lib/python2.7/json/encoder.py", line 201, 
        in encode, chunks = self.iterencode(o, _one_shot=True), File "/usr/lib/python2.7/json/encoder.py", line 264, 
        in iterencode, return _iterencode(o, 0),UnicodeDecodeError: 'utf8' codec can't decode byte 0xf6 in position 1: invalid start byte,

I don't understand clearly how encoding works, but I assume there is a missing configuration somewhere