Unexpected message redelivery

I'm using Sun One Message Queue 3.0 Platform Edition.

Problem : When my client app receives messages from the message broker, It got the same message serveral times.

Enviroment : I use the single receiver mode on the destination queue and my client appl sets the transaction flag to false and ACK to Session.AUTO_ACK when it create the receiver.eg. Session _sess = _conn.createQueueSession(false, Session.AUTO_ACKNOWLEDGE);

Will the message server delete the message when the receiver's receive method called in the sychronize receiving mode? I read this on the developer's guide, but it doesn't work well with my program. This condition occurs after two weeks testing.

Can somebody help me?

[757 byte] By [707859] at [2007-11-25 8:12:23]