The jndi name you are using for lookup is wrong. You can use the jmx-console to check the jndi names for the beans http://community.jboss.org/wiki/DisplayTheJNDITreeWithTheJMXConsole
Also take a look at this doc which tells how to override the jndi names and what their default syntax is http://docs.jboss.org/ejb3/docs/tutorial/1.0.7/html/JNDI_Bindings.html