yes, you are right, when I use jbossall-client.jar in an external client, it is fine. actually I need to use some EJB lookup-specific jar/jars (e.g. jnp-client.jar, jboss-je22.jar, etc.) within my web application. I tried to use some other jars combination instead of use the big jbossall-client.jar, but it ended up giving me the same error especially if I use jnp-client.jar. I thought the default classloading sequence for a web application is web libraries first, then tomcat libraries and jboss libraries. So before my war is deployed, everything is fine with JBoss, when JBOSS is trying to deploy my war file in a isolated web application scope, it gets jbossall-client.jar loaded first, which might contains some implementation classes with different version of dependencies classes from server side version of dependencies classes I guess. then there is conflicts. That's my thoughts about the issue, but I don't how to fix it. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4075022#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...