I would suspect a corrupted JAR file. The error means that the class file it was attempting to load (probably the Driver class) is not a valid class file. Another possibility could be that the JAR file was compiled with a more recent version of the java compiler (such as 1.5) and you are running it with an older JVM (such as 1.4). Also, not sure what your post has to do with the JBoss Portal, you should have placed this post in the Installation, Configuration & DEPLOYMENT forum. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4111738#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...