This usually occurs when you have either multiple oracle jar files (for example one in the server/lib directory and one in your EAR/WAR). Can you verify that you only have one copy of the driver? The other reason is that you are attempting to use the DS outside of JBoss (ie remote client). Can you post your *-ds.xml file? View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4008823#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...