i followed your tutorial
my problem is that the threads created newer stop when I call timer.cancel();
it looks like http://jira.jboss.com/jira/browse/JBAS-1690?page=all
am I right?
yes, very likely you have the same problem described in jira.
the simple solution though can be if you do not care about transactions - just switch them off (set the trans-attribute in your ejb-jar.xml to NotSupported) for the methods which are setting timers on and off.