Java EE (Java Enterprise Edition) General Discussion

I have created my first jpa web application, all goes well but now I have to implement a remove operation on a mapped object. But when I call EntityManager.remove on it, I get this excetpion:

java.lang.IllegalArgumentException: Entity must be managed to call remove: Abba Pino, try merging the detached and try the remove again.

the guilty code is this:

private void eliminaCliente(Evento evento) {
		Cliente cliente = this.finestraCliente.getCliente();
    	ClienteFacade facade = new ClienteFacade();
    	try {
			facade.getEm().getTransaction().begin();
			facade.getEm().merge(cliente);
			facade.getEm().remove(cliente);
			facade.getEm().flush();
		} catch(PersistenceException e) {
			String messaggio;
			if(e.getCause() instanceof ConstraintViolationException) { // vincolo di integrità violato
				messaggio = "Impossibile completare l'operazione a causa della violazione di un vincolo di integrità:\n---> ";
				messaggio += e.getCause().getCause().getMessage();
			} else // errore generico
				messaggio = e.getMessage();
			apriFinestraMessaggio(evento, messaggio);
		} finally {
			facade.getEm().close();
		}
	}

as you can see, I call the merge method on my detached entity before calling remove. Why doesn't it work?