Instantiation of models from xml string broken

/usr/local/lib/python2.7/dist-packages/gillespy/gillespy.pyc in from_string(cls, string)
    548         """ Intializes the document from an exisiting native StochKit XML 
    549         file read from disk. """
--> 550         root = etree.fromString(string)
    551 
    552         md = cls()

AttributeError: 'module' object has no attribute 'fromString'
