What version of JBoss are you using?
I'm using JBoss 3.0.2.
I don't know if it is your problem but I found that if you are using applet, the browser destroy the applet when you leave the web page. After you are not able to connect to the UIL service again.
Internaly the UIL service destroy a ThreadGroup. The following lines may help:
org.jboss.mq.Connection.threadGroup = new ThreadGroup("JBossMQ Client Threads");