No, what's wrong is that the web console is an orphan and no-one has made any effort to keep it up-to-date or even verify that it works in any given JBoss AS release. Personally, I never use it.
Try putting <JBOSS_HOME>\client\jboss-common-client.jar in your classpath.
Thanks. Shouldn't this be included in the JBoss distribution's classpath?