You mentioned editing the jndi.properties file on the 10... address. If you are talking about the conf/jndi.properties file, please remove your changes; they will break all sorts of things and are almost certainly the cause of your NameAlreadyBoundException.
Your problem is likely that your network is not allowing multicast communication between the two networks. Solutions are:
1) Get IT to allow the multicast traffic to pass.
2) Use non-multicast based configurations for the clustering traffic. The deploy/cluster-service.xml and deploy/tc5-cluster.sar/META-INF/jboss-service.xml files include example TCP-based configurations. You can uncomment and modify those for your environment, and comment out the UDP-based configurations above them.