Google Adwords traffic estimates - traceback

Traceback (most recent call last):
  File "traffictest.py", line 47, in <module>
    estimates = estimator_service.EstimateKeywordList(kwds)
  File "/path/to/venv/lib/python2.5/site-packages/adspygoogle/adwords/TrafficEstimatorService.py", line 162, in EstimateKeywordList
    return self.__service.CallMethod(method_name, (new_data))
  File "/path/to/venv/lib/python2.5/site-packages/adspygoogle/adwords/AdWordsWebService.py", line 255, in CallMethod
    self.__ManageSoap(buf, start_time, stop_time, error)
  File "/path/to/venv/lib/python2.5/site-packages/adspygoogle/adwords/AdWordsWebService.py", line 125, in __ManageSoap
    raise e
adspygoogle.adwords.AdWordsErrors.AdWordsRequestError: Code 94: Must specify a client in order to do traffic estimates.