org.jboss.mx.server.InvocationContext uses the ClassLoader.loadClass() call rather than Class.forName(). Due to a behavioral change from Java 5 to Java 6, this call now throws a ClassNotFoundException when that class is of an array type, e.g. "[Ljava.lang.String;".
The situation is the same as the one described here: https://jira.jboss.org/jira/browse/JBRULES-1553