Did you figure this out? I want to do the same, I succeeded with another piece of code I have found there:
but I would like to use jsonrpclib to make the code easier to read and less complicated. I also want to use jsonrpclib to have a server running on my pi to switch on and off the light in my living room. Long story short I want a cinema button on my XBMC remote control to switch off the big lights and put the small ones when I run a movie :) I don't want to use different jsonrpc lib/scripts and jsonrpclib looks perfect for what I have to do.
>>> import jsonrpclib
>>> print server.Player.GetActivePlayers()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python2.7/dist-packages/jsonrpclib/jsonrpc.py", line 276, in __call__
    return self.__send(self.__name, kwargs)
  File "/usr/local/lib/python2.7/dist-packages/jsonrpclib/jsonrpc.py", line 224, in _request
    response = self._run_request(request)
  File "/usr/local/lib/python2.7/dist-packages/jsonrpclib/jsonrpc.py", line 254, in _run_request
    return_obj = loads(response)
  File "/usr/local/lib/python2.7/dist-packages/jsonrpclib/jsonrpc.py", line 507, in loads
    result = jloads(data)
  File "/usr/local/lib/python2.7/dist-packages/jsonrpclib/jsonrpc.py", line 105, in jloads
    return json.loads(json_string)
  File "/usr/lib/python2.7/json/__init__.py", line 338, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python2.7/json/decoder.py", line 365, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python2.7/json/decoder.py", line 383, in raw_decode
    raise ValueError("No JSON object could be decoded")
ValueError: No JSON object could be decoded