smack error in pubsub subscribe response

Hi, this is my first post here and my english is not very good, so sorry for that
I'm working with a pubsub node, which is in authorize mode.
i make a StanzaListener on the owner of the node to authorize the subscription of users:

(i think the next code is ok, but i put it because i think it can help to understand and i dont know if this is the best way to do it)

StanzaListener myListener = new StanzaListener() {            public void processPacket(Stanza packet) {               for(ExtensionElement extension : packet.getExtensions())               {                    switch (extension.getNamespace())                    {                         ...                         case "jabber:x:data":                            Form form=Form.getFormFrom(packet);                            if (form.getField("FORM_TYPE").getValues().get(0).equals("http://jabber.org/protocol/pubsub#subscribe_authorization"))                            {                                Form answer = form.createAnswerForm();                                for (FormField field : answer.getFields())                                {                                    switch(field.getVariable())                                    {                                        case "pubsub#allow":                                            //I know, i accept all users for know                                            field.addValue("true");                                            break;                                        case "FORM_TYPE":                                            break;                                        default:                                            field.addValues(form.getField(field.getVariable()).getValues());                                    }                                }                                Message respuesta = new Message(packet.getFrom());                                respuesta.setFrom(packet.getTo());                                respuesta.setStanzaId(packet.getStanzaId());                                respuesta.addExtension(answer.getDataFormToSend());                                try {                                    connection.sendStanza(respuesta);                                } catch (SmackException.NotConnectedException ex) {                                    Logger.getLogger(Xmpp.class.getName()).log(Level.SEVERE, null, ex);                                }                                break;                             }                             ...

The problem is that when a user try to subscribe to the node, with this code:

LeafNode node = pubsubManager.getNode("thePubsubNode");
node.addItemEventListener(new ItemPubsubListener());
node.subscribe("validUser@validServer");

it gets this message error in the console:

Connection closed with error

java.lang.ClassCastException: org.jivesoftware.smack.packet.DefaultExtensionElement cannot be cast to org.jivesoftware.smackx.pubsub.NodeExtension

    at org.jivesoftware.smackx.pubsub.provider.EventProvider.createReturnExtension(Eve ntProvider.java:39)

    at org.jivesoftware.smackx.pubsub.provider.EventProvider.createReturnExtension(Eve ntProvider.java:34)

    at org.jivesoftware.smack.provider.EmbeddedExtensionProvider.parse(EmbeddedExtensi onProvider.java:108)

    at org.jivesoftware.smack.provider.EmbeddedExtensionProvider.parse(EmbeddedExtensi onProvider.java:84)

    at org.jivesoftware.smack.provider.Provider.parse(Provider.java:35)

    at org.jivesoftware.smack.util.PacketParserUtils.parseExtensionElement(PacketParse rUtils.java:929)

    at org.jivesoftware.smack.util.PacketParserUtils.addExtensionElement(PacketParserU tils.java:1060)

    at org.jivesoftware.smack.util.PacketParserUtils.parseMessage(PacketParserUtils.ja va:287)

    at org.jivesoftware.smack.util.PacketParserUtils.parseStanza(PacketParserUtils.jav a:151)

    at org.jivesoftware.smack.AbstractXMPPConnection.parseAndProcessStanza(AbstractXMP PConnection.java:956)

    at org.jivesoftware.smack.tcp.XMPPTCPConnection.access$500(XMPPTCPConnection.java: 140)

    at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.parsePackets(XMPPTCPC onnection.java:989)

    at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.access$300(XMPPTCPCon nection.java:944)

    at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader$1.run(XMPPTCPConnecti on.java:959)

    at java.lang.Thread.run(Thread.java:745)

i dont receive the answer with the approval notification in the smack debug window, and i cant make a StanzaListener, because the error occur before

I'm using smack 4.1.4, on a 15.06 ejabberd server (draugr.de)

thanks in advance and if you need more information just tell me