I am also quite new to java and eclipse, but I think this might help: You have to take care of the following fact: when you are compiling the source-code in eclipse, then eclipse will use the classpath that you have specified in eclipse (I guess, that's stored in your workspaces .classpath file) when you deploy your project to an applicationserver, the applicationserver does of course not know anything about your eclipse classpath. so you have following options (AFAIK): * tell eclipse to bundle your external jar into your .ear (or .war) | * let the applicationserver know your external .jar View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4135840#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...