XMPPError: not-authorized - auth android

I want to send a chat message to a group. But I cannot join this particular room from android app, I use openfire .. every time I get

XMPPError: not authorized

Auth error when I try to join the room .. Please answer. Below is the code:

MultiUserChatManager manager = MultiUserChatManager.getInstanceFor(connection);
MultiUserChat muc2 = manager.getMultiUserChat("testroom@conference.stag-api.artistaloud.com");
            try {
                muc2.join(fromName);
            }
            catch (Exception e){
                e.printStackTrace();
            }