TypeError when trying to call National Rail SOAP API via Node

I'm trying to access the National Rail API using node-soap.

Documentation is here: http://ift.tt/16YQLIF

I am new to SOAP so this might not be an issue with the API. I am getting a TypeError with whatever I attempt...

TypeError: Cannot read property 'Body' of undefined

Here is the code I am using to try and make a call:

var soap = require('soap');
var url = 'http://ift.tt/1vbtHvu';
var soapHeader = '<com:AccessToken>MY_TOKEN</com:AccessToken>';

soap.createClient(url, function(err, client){

  var args = {
    numRows : 10,
    crs : 'LAN'
  };

  client.addSoapHeader(soapHeader);

  client.GetDepartureBoard(args, function(err, result){
    if(err){
      console.log('error!');
      throw err;
    }
    console.log(result);
  });  
});

Using node-soap I can also get the request envelope, this is the contents:

<soap:Envelope
    xmlns:soap="http://ift.tt/sVJIaE"
    xmlns:xsi="http://ift.tt/ra1lAU"
    xmlns:tns="http://ift.tt/1vbtHvx"
    xmlns:tok="http://ift.tt/16YQLYY"
    xmlns:ct="http://ift.tt/1vbtHLL"
    xmlns:ldbt="http://ift.tt/12WZM2O"
    xmlns:ldbt2="http://ift.tt/1vbtFUh">
    <soap:Header>
        <com:AccessToken>MY_TOKEN</com:AccessToken>
    </soap:Header>
    <soap:Body>
        <tns:GetDepartureBoardRequest
            xmlns:tns="http://ift.tt/1vbtHvx"
            xmlns="http://ift.tt/1vbtHvx">
            <tns:numRows>10</tns:numRows>
            <tns:crs>LAN</tns:crs>
        </tns:GetDepartureBoardRequest>
    </soap:Body>
</soap:Envelope>