Jboss7 里面 com.sun.proxy.$Proxy0 cannot be cast to com.ejb.impl.HelloWorldImpl

Question

Hashtable jndiProperties = new Hashtable();
jndiProperties.put(Context.URL_PKG_PREFIXES, "org.jboss.ejb.client.naming");

 try {
    Context  initial=new InitialContext(jndiProperties);
    Object hello=
            initial.lookup
            ("ejb:/hello/HelloWorldImpl!com.ejb.HelloWorld");

    HelloWorldImpl ho=(HelloWorldImpl)hello;
    System.out.print(ho.Hello(""));

出现错误如题。。麻烦大神指点一下。我刚学EJB.