(1) Working environments
OS : WindowsNT4.0 + SP5
Browser : Netscape4.7
Java Plug-in : Java Plug-in 1.1.3_001

(2) Phenomenon
Several JPanels puts on JApplet using card layout.
Each JPanel transitions one after another when some event occurs.
Then following exception occurs.

Exception occurred during event dispatching:
java.lang.NullPointerException: invalid peer
at sun.awt.windows.WWindowPeer$FocusOnActivate.dispatch(WWindowPeer.java:130)
at java.awt.EventDispatchThread.run(Compiled Code)

However this exception not occurs when using Java Plug-in 1.1.3.

(3) Questions
There are some questions about this exception.
What the case this exception occurs?
Our JApplet program is running, even if this exception occurs. If ignore this
exception, something problem happen?

Our JApplet program makes my user, IBM Japan, Ltd. I have to yet get this one.
I sorry that I don't give it.