In the hopes of benefitting anyone else who runs into this error -- it was an issue with the file versions. When I installed JBoss 4.0.5, and the latest version of the cache and aop software, I needed to build from the lib-50 stuff from the aop install and the cache install. I was attempting to build from the JBoss 4.0.5 server lib jars. I ended up copying the lib-50 jars to JBoss... /server/default/lib. I'm hoping I'll also be able to run now!! J View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4003855#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...