AFAIK, JBoss AS 5.1 requires JDK 6. Are you using JDK 5? View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4254519#4254519 Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&p=4254519