Hello: I am developing an application using JBoss 4.0.5. JBoss is running in cluster and is offering support for ejb3. A test client is supposed to contact the ejb through HAJNDI. It was working OK using JNDI, but when trying to contact the ejb using HAJNDI I had exactly the same problem as you do. Luckily I was able to solve it adding some libraries to my client´s classpath. I give you the whole list of libraries I was using: concurrent.jar jboss.jar jboss-annotations-ejb3.jar jboss-aop-jdk50.jar jboss-aspect-library-jdk50.jar jboss-common.jar jboss-ejb3.jar jboss-ejb3x.jar jboss-j2ee.jar jboss-remoting.jar jbosssx.jar jboss-transaction.jar jnpserver.jar junit.jar The ones I was missing (and caused the hajndi problem) were: jbossha.jar jboss-serialization.jar. I hope that can help. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4008449#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...