After trying a number of things, I've found that the new web module was trying to use TreeCache from the newer version of JBoss. Importing derby, jgroups, jboss-common-core (2.2.8), jcip-annotations, c3p0, and jbosscache-core (2.2.0) through the manifest file seem to cause the problem. I'm trying to repackage my EAR file with these JARs in the individual WAR file and not the top-level EAR. Doing so lets my MDB start up, but its not yet loading the TreeCache again. Any ideas why TreeCache might cause this problem? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4203206#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...