node-soap: SOAP-Client for Sympa returns syntax error

I'm trying to excecute a SOAP-Method of the Sympa-demo-server within my node.js-script with the help of node-soap:

var soap = require('soap'),
    url = 'http://demo.sympa.org/sympa/wsdl',
    emailAddress = 'mail@domain.tld',
    passwordPlain = 'password';

var args = {email: emailAddress, password: passwordPlain};
var cookieLogin = '';
soap.createClient(url, function(err, client) {
    client.login(args, function(err, result) {
        if (err) {
            console.error(err);
            console.log(args);
        } else {
            cookieLogin = result;
            console.log(result);
        }
    });
});

The script is obtains the WSDL pretty good but excecuting the service "login" returns

[Error: syntax error]

I think the parameters are spelled correctly as described in the WSDL.

Does anyone have an idea which is my syntax-error? I my opinion it must be my argument-object, but I'm out of ideas...

UPDATE: As mentioned below it is just Sympa is not responding according to it's WSDL. So if you are using a strongly typed programming-language you have to go from scratch an send HTTP-requests and evaluate the HTTP-Answers by yourself.