Thanks alot got it working at work as well!
There is probably some incopatibility between jdk5 javax.management.* and jboss javax.management.* classes.
If you remove javax.management.* classes from jdk5/jre/rt.jar persistence will work with jdk5, too, so this is not a problem of persistence really.
We'll further investigate this, thanks for the report.
There is a bug in jdk5 ModelMBeanInfoSupport.getDescriptors(null) implementation. I've made a work-around for jboss v3.2.7/v4.0.1