If a XML-RPC server returns an error page without a content-length header (for example with "transfer-encoding: chunked" instead), the method "single_request" in xmlrpclib doesn't read the response before raising a ProtocolError.
If this happens and the http connection is reused, the response is in a broken state and the next request will trigger a ResponseNotReady exception in httplib.

Possible solutions would be to explicitly close the response before raising the ProtocolError or read the response for chunked encoding.