Install latest jdk 6u4 b03 nightly build, run appletviewer on any demo applet and you'll see the following NPE.
This problem is applicable to all platforms.

D:\testclasses>"F:\Program Files\Java\jdk1.6.0_04\bin"\appletviewer "F:\ProgramFiles\Java\jdk1.6.0_04\demo\applets\Clock\example1.html"
Exception in thread "main" java.lang.NullPointerException
        at sun.applet.AppletPanel.init(AppletPanel.java:213)
        at sun.applet.AppletViewer.<init>(AppletViewer.java:177)
        at sun.applet.StdAppletViewerFactory.createAppletViewer(AppletViewer.jav
a:82)
        at sun.applet.AppletViewer.parse(AppletViewer.java:1122)
        at sun.applet.AppletViewer.parse(AppletViewer.java:1056)
        at sun.applet.Main.run(Main.java:138)
        at sun.applet.Main.main(Main.java:80)