Invalid control character at: line 3 column 203 (char 255)

I have followed the set-up procedure in the Wiki. I receive the following error when running the supplied test. Any suggestions are greatly appreciated!

{
  "errorMessage": "Invalid control character at: line 3 column 203 (char 255)",
  "errorType": "JSONDecodeError",
  "stackTrace": [
    [
      "/var/task/haaska.py",
      106,
      "event_handler",
      "config = Configuration('config.json')"
    ],
    [
      "/var/task/haaska.py",
      80,
      "__init__",
      "self._json = json.load(f)"
    ],
    [
      "/var/lang/lib/python3.6/json/__init__.py",
      299,
      "load",
      "parse_constant=parse_constant, object_pairs_hook=object_pairs_hook, **kw)"
    ],
    [
      "/var/lang/lib/python3.6/json/__init__.py",
      354,
      "loads",
      "return _default_decoder.decode(s)"
    ],
    [
      "/var/lang/lib/python3.6/json/decoder.py",
      339,
      "decode",
      "obj, end = self.raw_decode(s, idx=_w(s, 0).end())"
    ],
    [
      "/var/lang/lib/python3.6/json/decoder.py",
      355,
      "raw_decode",
      "obj, end = self.scan_once(s, idx)"
    ]
  ]
}

have the same error - did you find a solution?