When you fire up Eclipse, which Java runtime is it using? Check /Applications/.../eclipse.ini - is there a -vm section which points to a specific Java version? If not, then start Eclipse and go into Help > About > configuration to see what JVM is being used to run Eclipse. If you want to force Eclipse to start w/ 6 instead of 5 (or vice versa) edit your eclipse.ini file: http://wiki.eclipse.org/IRC_FAQ#How_do_I_start_Eclipse.3F When you start JBoss AS 5.0.1, are you starting it from within Eclipse? If so, open the Debug view and right-click the thread, then select Properties. What JVM is being used there? I'm *guessing* there's a mismatch somewhere here, but I could be chasing my tail here. :) You might have to clean out old .class files from your project(s) and recompile w/ a 5.0 JVM? View the original post : http://www.jboss.org/index.html?module=bb&op=viewtopic&p=4236782#... Reply to the post : http://www.jboss.org/index.html?module=bb&op=posting&mode=reply&a...