Here's the output from the java Console:

java.lang.NullPointerException
	at sun.plugin.util.GrayBoxPainter.paintGrayBox(GrayBoxPainter.java:534)
	at sun.plugin.util.GrayBoxPainter.repaintGrayBox(GrayBoxPainter.java:499)
	at sun.plugin.util.GrayBoxPainter.progressFinish(GrayBoxPainter.java:411)
	at sun.plugin.util.ProgressMonitor.unregisterSource(ProgressMonitor.java:174)
	at sun.net.ProgressSource.finishTracking(ProgressSource.java:137)
	at sun.plugin.security.PluginClassLoader.updateJarProgress(PluginClassLoader.java:450)
	at sun.plugin.security.PluginClassLoader.addJar(PluginClassLoader.java:428)
	at sun.applet.AppletPanel.loadJarFiles(AppletPanel.java:755)
	at sun.plugin.AppletViewer.loadJarFiles(AppletViewer.java:1353)
	at sun.applet.AppletPanel.runLoader(AppletPanel.java:638)
	at sun.applet.AppletPanel.run(AppletPanel.java:319)
	at java.lang.Thread.run(Thread.java:595)
Exception in thread "Thread-201" java.lang.NullPointerException
	at sun.plugin.util.GrayBoxPanel.paint(GrayBoxPanel.java:103)
	at sun.plugin.util.GrayBoxPainter.paintGrayBox(GrayBoxPainter.java:545)
	at sun.plugin.util.GrayBoxPainter.repaintGrayBox(GrayBoxPainter.java:499)
	at sun.plugin.util.GrayBoxPainter.showLoadingError(GrayBoxPainter.java:149)
	at sun.plugin.AppletViewer.showAppletException(AppletViewer.java:1873)
	at sun.applet.AppletPanel.runLoader(AppletPanel.java:662)
	at sun.applet.AppletPanel.run(AppletPanel.java:319)

It seems to happen more after an 'x'.

Java(TM) Plug-in 1.5.0-beta3-b57

Mozilla 1.7a
Mozilla/5.0 (X11; U; SunOS sun4u; en-US; rv:1.7a) Gecko/20040227
bash-2.05$ uname -a
SunOS class-04 5.9 Generic_112233-12 sun4u sparc SUNW,Sun-Blade-100