In netscape's Release Notes :

     * You should set the CLASSPATH environment variable only if you need
       to install special Java files in Communicator. Communicator uses
       CLASSPATH to find local .class files. If CLASSPATH is set in the
       user's environment, only the .jar files and directories specified
       in the CLASSPATH are searched. If you set your CLASSPATH variable,
       you need to make sure that each .jar file in
       $MOZILLA_HOME/java/classes is listed individually in your
       CLASSPATH.

set CLASSPATH to acivate java:

setenv CLASSPATH /opt/netscape/java/classes/ifc11.jar:/opt/netscape/java/classes/iiop10.jar:/opt/netscape/java/classes/jae40.jar:/opt/netscape/java/classes/java40.jar:/opt/netscape/java/classes/jio40.jar:/opt/netscape/java/classes/joptio40.jar:/opt/netscape/java/classes/jsd10.jar:/opt/netscape/java/classes/ldap40.jar:/opt/netscape/java/classes/resource.jar:/opt/netscape/java/classes/scd10.jar