Java SE (Java Platform, Standard Edition)

I'm trying to set up the Java Communications API on Linux, and I can't seem to get it to find my javax.comm.properties file. I've put comm.jar in $JDK_HOME/jre/lib/ext and the properties file in $JDK_HOME/jre/lib and $JDK_HOME/lib (using JDK 1.4.2_08).

I set my CLASSPATH to "$JDK_HOME/jre/lib/ext/comm.jar:BlackBox.jar" and when I try to run BlackBox, I get:
javax.comm: Error loading javax.comm.properties!
null

java.io.IOException: javax.comm: platform driver class name = null
(Check 'driver' property in javax.comm.properties)

at javax.comm.CommPortIdentifier.loadDriver(CommPortIdentifier.java:244)
at javax.comm.CommPortIdentifier.<clinit>(CommPortIdentifier.java:109)
at BlackBox.main(Unknown Source)
Exception in thread "main" java.lang.UnsatisfiedLinkError: isSessionActive
at com.sun.comm.SunrayInfo.isSessionActive(Native Method)
at com.sun.comm.Portmapping.registerCommPorts(Portmapping.java:155)
at com.sun.comm.Portmapping.refreshPortDatabase(Portmapping.java:100)
at javax.comm.CommPortIdentifier.<clinit>(CommPortIdentifier.java:138)
at BlackBox.main(Unknown Source)

Any idea what's wrong?