This error message often indicates that your session bean (stateless or stateful) is missing an interface (local or remote).
    @Local
    public interface Register {
        public boolean register();
    }

    public interface RegisterAction implements Register
      ...
This is an EJB3.0 requirement. More information, including the difference between stateless and stateful beans, and the difference between local and remote interfaces, can be found in the Part IV of the Java EE 5 Tutorial.