addUserToGroup breaks in Python: Invalid element in com.atlassian.jira.rpc.soap.beans

The Python call to this SOAP method:

self.soap.addUserToGroup(self.auth, remoteGroup, remoteUser)

results in:

File "jirascript.py", line 108, in ?
script.createNewProject(sys.argv[2], sys.argv[3], sys.argv[4])
File "jirascript.py", line 76, in createNewProject
self.soap.addUserToGroup(self.auth, remoteGroup, userR)
File "c:\python24\Lib\site-packages\SOAPpy\Client.py", line 470, in _call_
return self.__r_call(*args, **kw)
File "c:\python24\Lib\site-packages\SOAPpy\Client.py", line 492, in __r_call
self._hd, self._ma)
File "c:\python24\Lib\site-packages\SOAPpy\Client.py", line 406, in __call
raise p
SOAPpy.Types.faultType: <Fault soapenv:Server.userException: org.xml.sax.SAXException: Invalid element in com.atlassian.jira.rpc.soap.beans.
RemoteGroup - email: <SOAPpy.Types.structType detail at 29991600>: {'hostname': 'bruwa116', 'faultData': <SOAPpy.Types.structType faultData
at 29991680>: {'exception': None, 'message': 'Invalid element in com.atlassian.jira.rpc.soap.beans.RemoteGroup - email'}}>