smack+ejabberd in Ubuntu 12.04

Hi,

I'm trying to write a simple XMPP client to communicate with the Ejabberd server in Ubuntu 12.04. But i've always a problem during the login step. my code is like that:

    ConnectionConfiguration config = new ConnectionConfiguration("127.0.0.1",5222,"localhost");

    connection = new XMPPConnection(config);

    connection.connect();

    connection.login(toto, toto); 

    manager = new FileTransferManager(connection);

    }

and the result is:

<iq id="IJc5n-11" to="toto@localhost/Smack" from="toto@localhost" type="error">

  <ping xmlns="urn:xmpp:ping"/>

  <error code="503" type="CANCEL">

    <service-unavailable xmlns="urn:ietf:params:xml:ns:xmpp-stanzas"/>

  </error>

</iq>

anyoen could tell me what's exactly the problem and how can I fix it?  Thank you very much.