Duplicate message received

I found if the Recevier and Sender start almost the same time. The Receiver will receiver the same message twise. I have included my Testing program run by
java -classpath .;..\activemq-3.1.jar;..\lib\geronimo-spec-jms-1.1-rc4.jar;..\lib\geronimo-spec-j2ee-management-1.0-rc4.jar;..\lib\commons-logging-1.0.3.jar;..\lib\log4j-1.2.8.jar;..\lib\concurrent-1.3.4.jar;..\conf;..\lib\spring-1.2.2.jar TestJmsSender

I have test by restarted the program ~10 times and around 40% chance of have the error of receiver rec same message twise