You are using JDK6 in which this is a known issue. The readme in JBoss says this: anonymous wrote : If you still have problems using JBoss with a Sun Java 6 runtime, you may want to set -Dsun.lang.ClassLoader.allowArraySyntax=true, as described in JBAS-4491 Pass that parameter to the JVM through the run.bat By the way, i would recommend that you upgrade to JBoss-5.0 GA which has been released http://www.jboss.com/index.html?module=bb&op=viewtopic&t=146773 View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4206153#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...