Hmm, I wonder if the web console even knows how to work with JBoss Messaging? I bet the JSP compiler couldn't compile tha JSP because it was using old JBossMQ classes. I was right! The Topic jsp inherits form org.jboss.mq.server.jmx.TopicMBean which is part of JBosMQ which is no longer present.
My recommendation: forget web-console, It is an old apps that has not been updated in years. Use Embedded Jopr instead. though you will have to download the source code and compile it to get a 5.0.x-friendly version.
Peter, thanks for taking the time to respond.
I'm able to use the web console on another computer running JBoss, and see the details of a given Topic without getting any error messages, but that's actually an earlier version, version 4.2.3.GA. I guess I should switch to that version, but I will take a look at Jopr, thanks again.
Of course it works on 4.2.3 - that version still uses JBossMQ.