The GrayBoxPainter in the plug-in is notorious for the exceptions it prints to the Java Console. The root cause of these exceptions is the fact that this class is generally used in a thread-unsafe manner, which is at least partially unavoidable (at least, not without large restructuring of the code) due to how the download progress callbacks work. Here, however, is a stack trace from the new Java Plug-In where such an error causes an applet to not load properly:

java.lang.NullPointerException: component argument pData
at sun.java2d.windows.GDIRenderer.doFillRect(Native Method)
at sun.java2d.windows.GDIRenderer.fillRect(GDIRenderer.java:129)
at sun.java2d.pipe.ValidatePipe.fillRect(ValidatePipe.java:58)
at sun.java2d.SunGraphics2D.fillRect(SunGraphics2D.java:2274)
at sun.plugin.util.GrayBoxPanel.paint(GrayBoxPanel.java:133)
at sun.plugin.util.GrayBoxPainter.paintGrayBox(GrayBoxPainter.java:363)
at sun.plugin.util.GrayBoxPainter.repaintGrayBox(GrayBoxPainter.java:313)
at sun.plugin.util.GrayBoxPainter.access$200(GrayBoxPainter.java:37)
at sun.plugin.util.GrayBoxPainter$GrayBoxProgressListener.progressFinish(GrayBoxPainter.java:491)
at sun.plugin.util.EventMulticaster.progressFinish(EventMulticaster.java:114)
at sun.plugin.util.ProgressMonitor.unregisterSource(ProgressMonitor.java:176)
at sun.net.ProgressSource.finishTracking(ProgressSource.java:137)
at sun.net.www.http.KeepAliveStream.close(KeepAliveStream.java:91)
at sun.net.www.MeteredStream.justRead(MeteredStream.java:75)
at sun.net.www.MeteredStream.read(MeteredStream.java:117)
at java.io.FilterInputStream.read(FilterInputStream.java:116)
at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.read(HttpURLConnection.java:2385)
at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
at java.io.BufferedInputStream.read1(BufferedInputStream.java:258)
at java.io.BufferedInputStream.read(BufferedInputStream.java:317)
at sun.plugin2.applet.Applet2ClassLoader.getBytes(Applet2ClassLoader.java:549)
at sun.plugin2.applet.Applet2ClassLoader.access$700(Applet2ClassLoader.java:55)
at sun.plugin2.applet.Applet2ClassLoader$2.run(Applet2ClassLoader.java:224)
at java.security.AccessController.doPrivileged(Native Method)
at sun.plugin2.applet.Applet2ClassLoader.findClass(Applet2ClassLoader.java:221)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:252)
at sun.plugin2.applet.Applet2ClassLoader.loadCode(Applet2ClassLoader.java:864)
at sun.plugin2.applet.Applet2Manager.createApplet(Applet2Manager.java:2835)
at sun.plugin2.applet.Applet2Manager.access$2000(Applet2Manager.java:87)
at sun.plugin2.applet.Applet2Manager$AppletExecutionRunnable.run(Applet2Manager.java:1399)
at java.lang.Thread.run(Thread.java:619)

We need to guard against RuntimeExceptions propagating out of the GrayBoxPainter and use Trace.ignoredException() to display them, so that if tracing is turned off they don't pollute the Java Console output.