exceptions thrown out from Liveconnect applet

jdk1.6.0-ea-b55, S10U1 b15, Mozilla 20050816.

reproduce steps:

1. start Mozilla
2. load the applet http://quarterfinal.prc/liveconnect/java2javascript/Test1.html
3. click the button on the page immediately

exepected result:
an alert window pops up

actual result:
no alert window pups up
and following exceptions thrown out in the Java Console:

null
java.security.PrivilegedActionException: java.lang.reflect.InvocationTargetException
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.plugin.liveconnect.SecureInvocation$2.run(SecureInvocation.java:204)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.plugin.liveconnect.SecureInvocation.CallMethod(SecureInvocation.java:183)
    at sun.plugin.navig.motif.AThread.handleRequest(Native Method)
    at sun.plugin.navig.motif.AThread.JNIHandleLoop(AThread.java:35)
    at sun.plugin.navig.motif.AThread.run(AThread.java:27)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:585)
    at sun.plugin.javascript.invoke.JSInvoke.invoke(JSInvoke.java:19)
    at sun.reflect.GeneratedMethodAccessor3.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:585)
    at sun.plugin.javascript.JSClassLoader.invoke(JSClassLoader.java:44)
    at sun.plugin.liveconnect.PrivilegedCallMethodAction.run(SecureInvocation.java:572)
    ... 7 more
Caused by: java.lang.NullPointerException
    at Test1.alertWin(Test1.java:36)
    ... 17 more
[object Window]