I should also add that this code worked in JBoss 3.22 with Java 1.4.2
where there was no Sun RI in the environment, so I'm confident I am
adding the relationship correctly, if I could get the right class.
You can't when running under jdk1.5 as the RelationService is not a pluggable implementation detail. As far as i can see the extension mechanism does not apply to the jmx classes.