Answer
It appears that Netscape 6 fails to recognize the JAVA_HOME variable; hence, Netscape 6 is expecting to find the necessary ArcIMS Java Archive (JAR) files under the default Java 2 Runtime Environment (JRE) install location. To get around this, copy the JAR files from $AIMSHOME/Manager/lib to the default JRE install location.
On HP-UX:
/opt/java1.3/lib/ext
On Solaris:
/usr/j2se/jre/lib/ext