With the new generation java plugin of 1.6.0_10 or 1.6.0_11 we see the following error
with Firefox3.0.x on Win xp OR IE7 on Win xp and VISTA.

on client side java console:
Java version : 1.6.0_10
Proxy type : null
java.lang.NullPointerException
        at com.sun.portal.netlet.client.applet.NL30.l(NL30)
        at com.sun.portal.netlet.client.applet.NL30.<init>(NL30)
        at com.sun.portal.netlet.client.applet.NL43.<init>(NL43)
        at com.sun.portal.netlet.client.applet.NetletApplet.b(NetletApplet)
        at com.sun.portal.netlet.client.applet.NetletApplet.h(NetletApplet)
        at com.sun.portal.netlet.client.applet.NetletApplet.start(NetletApplet)
        at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)
Exception: java.lang.NullPointerException

Regarding the NPE while loading the applet, this is due to the applet not been able to read proxy config.
FYI, Refer related bug 6774243