On http://trailblazer.demo.jboss.com/EJB3Trail/serviceobjects/jmx/index.html
it says

public class CalculatorMBean implements Calculator

If I understand JMX correctly the naming conventions are reversed here. See http://java.sun.com/j2se/1.5.0/docs/guide/jmx/tutorial/essential.html#wp1053106

The interface should be suffixed MBean and not the implementation!

I also believe it only works if you do it correctly. So you will not be able to get the example working.