You are in the wrong forum.
Thanx for an answer - but isn't it the right one? - the question is not a jmx-tutorial related but about the JMX server implementation on JBoss. As I found out this time by playing with the working one - StandardMBean - the bean is loaded by jvm-standard classloader, sun.misc.Launcher$AppClassLoader, and not by the thread-context stored org.jboss.mx.loading.UnifiedClassLoader3 which really has an jboss-jmx.jar in it referred urls. I beleive that JBoss is fine and it's just my installation/mbean definition mistake - but, still, isn't that a right forum to ask? Anf if not - could U say - which one is?