The external RMI server and the Oracle JVM must use the same hostname/IP address in order for RMI to work . This is particularly important when the server has multiple interfaces.
The server name can be set in server.properties. The client name is set on install and can be changed by updating the table c$arnachm1.rmi_hostname (this table has a single row and column). To set the hostname use (as c$arnachm1):
update rmi_hostname set rmi_hostname = 'rmi_server.company.com';