The EJBException constructor that was introduced in EJB 2.0 (the one with a string and an enclosed exception) throws invisible exceptions in JBoss 2.4. So if you have an EJB that's failing silently check for these EJB 2.0 EJBExceptions and switch them to 1.1 constructors ! (until the RabbitHole arrives and presumably implements the EJB2.0 Exception properly)...
The Exception constructors in the newes jboss-j2ee.jar are o.k.. I checked this because I'd the same problem.
Make shure, that the correct jboss-j2ee.jar is the only one in Your classpath which contains this J2EE classes.