PubSubHubBub in Java: can't subscribe

Question

I'm trying to develop a simple Java PubSubHubBub application. I downloaded this sample code to test it, but when I try to subscribe I always get an error 409. Following PuSH specifications, I created my own feed at this link: receivetemplate.eu01.aws.af.cm/feed/

This is the code in the Test class for the subscriber:

package sub;

import java.net.InetAddress;

import PubSubHubbub.Web;
import PubSubHubbub.Subscriber;

public class Test {

    private static Web webserver;
    private static Subscriber sbcbr;
    private static String hostname = null;
    private static Integer webserverPort = 8080;

    private static void startServer(){
        try {
            webserver = new Web(webserverPort);

            sbcbr = new Subscriber(webserver);


            InetAddress addr = InetAddress.getByName("receivetemplate.eu01.aws.af.cm");
            hostname = addr.getHostName();

            System.out.println("http://" + hostname + "/");
            hostname = "http://" + hostname + "/";

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("WebServer can not start");
        }

    }

    public static void main(String[] args) {
        try {

               String hub = "http://pubsubhubbub.appspot.com/subscribe";
               String hub_topic = "http://receivetemplate.eu01.aws.af.cm/feed/";

               startServer();

               int statusCode = sbcbr.subscribe(hub, hub_topic, hostname, null, null);

               if (statusCode == 204){
                   System.out.println("the status code of the subscription is 204: the request was verified and that the subscription is active");
               } else if (statusCode == 202){
                   System.out.println("the status code of the subscription is 202: the subscription has yet to be verified (i.e., the hub is using asynchronous verification)");
               } else{
                   System.out.println("the status code of the subscription is:" + statusCode);   
               }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

If I replace hub_topic with http://pubsubhubbub-subscriber.appspot.com/ and if I pass pubsubhubbub-subscriber.appspot.com to InetAddress.getByName(), the response I get is 204 and everything works.

Can you give me some informations on what I'm doing wrong? Is there any error in my feed?