Traceback (most recent call last):
  File "dropbox_ul.py", line 6, in <module>
    response = client.put_file('/magnum-opus.txt', f)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/dropbox-1.4-py2.7.egg/dropbox/client.py", line 149, in put_file
    return RESTClient.PUT(url, file_obj, headers)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/dropbox-1.4-py2.7.egg/dropbox/rest.py", line 146, in PUT
    return cls.request("PUT", url, body=body, headers=headers, raw_response=raw_response)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/dropbox-1.4-py2.7.egg/dropbox/rest.py", line 113, in request
    raise ErrorResponse(r)
dropbox.rest.ErrorResponse: [401] 'Authentication failed'