because it has not yet been started, or was already stopped

com.vaadin.event.ListenerMethod$MethodException
Cause: java.lang.IllegalStateException: WEB9031: WebappClassLoader unable to load resource [consultorio.Area], because it has not yet been started, or was already stopped
at com.vaadin.event.ListenerMethod.receiveEvent(ListenerMethod.java:510)
at com.vaadin.event.EventRouter.fireEvent(EventRouter.java:164)
at com.vaadin.ui.AbstractComponent.fireEvent(AbstractComponent.java:1193)
at com.vaadin.ui.Button.fireClick(Button.java:539)
at com.vaadin.ui.Button.changeVariables(Button.java:206)

Causas 2:
Tenía q reiniciar el server, era problema de glassfish, por que no reconocia la entidad Area.