Hmmm, maybe you should stop mixing up jars? Stick to jars coming from a particular AS version and you should be fine.
Like Galder mentioned, packaging HA-JNDI in its own jar would not somehow eliminate class compatibility problems. Do not attempt to upgrade individual components within the AS unless you know exactly what you're doing. That said, upgrading components to a new major release will almost never work.
To answer your specific question, in AS5 and later, HA-JNDI is packaged in the jboss-as-cluster.jar (i.e. not separately), and requires several dependency jars.