Hello everyone and thank you for your quick reply Eduardo. Unfortunately I cannot send the logs or the configuration; the work I am engaged in is proprietary so I can share very little. But almost nothing has changed in our code that has been using wildfly-23 for some time. We are running wildfly standalone and I used standalone-full.xml as the template, just adding stuff for our JDBC driver and our JMS queues.
When I trapped the exception I got a stack trace that revealed it was deep in the wildfly code, starting at RemoteNamingProvider.java in the function getPeerIdentityForNaming. Tracking back into the project code it is the lookup function, which calls javx.naming.InitialContext.lookup.
I note from netstat that nothing seems to be listening on the port number I am using. Shouldn't wildfly be listening to it? Of course if it isn't for whatever reason then this might explain the client side error. But the server.log from wildfly seems to be clean.