OS: Win XP PRO
Java: jdk/jre 1.6.0, JMF 2.1.1e
Web Browser: IE 6.0 and Firefox 1.5.0.9

source code: Java Media Framework (JMF) 2.1 - Sample Code.
http://java.sun.com/products/java-me...yerApplet.java

html file (Note: you may change java_sound.wav to other audio/video files):
<html>
<applet code=SimplePlayerApplet width=320 height=300>
<param name=file value="java_sound.wav">
</applet>
</html>

Problem description
This applet runs well in IE or Firefox. However, when I click the Refresh button rapidly (as fast as I can), the Java Console

prints out the following message in most cases:
java.lang.NullPointerException
at sun.plugin.AppletViewer.loadJarFiles(Unknown Source)
at sun.applet.AppletPanel.runLoader(Unknown Source)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

From time to time, it prints out
java.lang.NullPointerException
at sun.plugin.AppletViewer.loadJarFiles(Unknown Source)
at sun.applet.AppletPanel.runLoader(Unknown Source)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at sun.plugin.viewer.WNetscapePluginObject$1.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

This problem is quite weird to me bacause SimplePlayerApplet.java is Sample Code of JMF.
Any ideas about how to fix that?
Thanks in advance!