After using NB on Windows Vista for some days without problems, Netbeans startet to crash when I changed from one 
document to another in the editor by clicking on the tabs.

Started NB from the command line. Got this error:

SCHWERWIEGEND [org.openide.util.RequestProcessor]
java.lang.AssertionError: CloneableEditorSupport.getOpenedPanes() must be called
 from AWT thread only
        at org.openide.text.CloneableEditorSupport.getOpenedPanes(CloneableEdito
rSupport.java:1059)
        at org.netbeans.modules.mobility.editor.DocumentPreprocessor.repaintDocu
ment(DocumentPreprocessor.java:214)
        at org.netbeans.modules.mobility.editor.DocumentPreprocessor.updateBlock
Chain(DocumentPreprocessor.java:206)
        at org.netbeans.modules.mobility.editor.DocumentPreprocessor.<init>(Docu
mentPreprocessor.java:117)
        at org.netbeans.modules.mobility.editor.pub.J2MEDataObject$J2MEEditorSup
port.createEditorKit(J2MEDataObject.java:346)
        at org.openide.text.CloneableEditorSupport.prepareDocument(CloneableEdit
orSupport.java:596)
        at org.openide.text.CloneableEditorSupport.prepareDocument(CloneableEdit
orSupport.java:540)
        at org.openide.text.CloneableEditor$DoInitialize.initNonVisual(Cloneable
Editor.java:309)
        at org.openide.text.CloneableEditor$DoInitialize.run(CloneableEditor.jav
a:261)
        at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:573)

[catch] at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java
:1005)