Can anyone tell me what the following error mean? and how to fix it?

I try to run the WidgetTest of visad's util package, but got the
following error

helen@virga [87] j/users/helen/VisAD/ava visad.util.WidgetTest
Exception in thread "main" java.lang.Error: Do not use
javax.swing.JFrame.setLayout() use
javax.swing.JFrame.getContentPane().setLayout() instead
        at javax.swing.JFrame.createRootPaneException(,
Compiled Code)
        at javax.swing.JFrame.setLayout(, Compiled Code)
        at visad.util.WidgetTest.main(, Compiled Code)

I got the same error as above when I am running VisAD on SGI Octane and
Windows 2000.
Please help me to fix the problem. Great thanks in advance.