Brian is correct, you cannot replace JBC 1.4.x with 3.x in JBoss AS 4.x. I thought you wanted to migrate from 1.4.x to 3.x in one of your custom apps and hence my comment earlier. If you have a webapp or an ear that directly interfaces with JBC and you want to use the new features in 3.x and still deploy in JBoss AS 4.2, have a look at this link. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4199201#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...