This exception is reported when starting Netbeans 
4.0 beta 2.  I started it while starting a number 
of other programs at the same time.  This, of 
course, changed the timing in the system.  I 
mention this because the problem might be a race 
condition (mutual exclusion).

Annotation: Exception occurred in Request 
Processor
java.lang.IllegalStateException: Duplicate pair 
in treePair1: SL[/Browsers/SwingBrowser pair2: SL
[/Browsers/SwingBrowser index1: 6 index2: 6 
item1: org.netbeans.core.ui.SwingBrowser@e580e1 
item2: org.netbeans.core.ui.SwingBrowser@e580e1 
id1: 17050f5 id2: d337d3
	at 
org.openide.util.lookup.ALPairComparator.compare
(ALPairComparator.java:52)
	at java.util.Arrays.mergeSort
(Arrays.java:1284)
	at java.util.Arrays.mergeSort
(Arrays.java:1296)
	at java.util.Arrays.sort(Arrays.java:1223)
	at java.util.Collections.sort
(Collections.java:159)
	at 
org.openide.util.lookup.InheritanceTree.retainAllI
nterface(InheritanceTree.java:751)
	at 
org.openide.util.lookup.InheritanceTree.retainAll
(InheritanceTree.java:183)
	at 
org.openide.util.lookup.DelegatingStorage.retainAl
l(DelegatingStorage.java:83)
	at 
org.openide.util.lookup.AbstractLookup.setPairsAnd
CollectListeners(AbstractLookup.java:238)
	at 
org.openide.util.lookup.AbstractLookup.setPairs
(AbstractLookup.java:203)
	at 
org.openide.util.lookup.AbstractLookup$Content.set
Pairs(AbstractLookup.java:885)
	at 
org.openide.loaders.FolderLookup$ProxyLkp.update
(FolderLookup.java:336)
	at 
org.openide.loaders.FolderLookup.createInstance
(FolderLookup.java:170)
	at 
org.openide.loaders.FolderInstance.defaultProcessO
bjects(FolderInstance.java:710)
	at 
org.openide.loaders.FolderInstance.access$000
(FolderInstance.java:68)
	at 
org.openide.loaders.FolderInstance$2.run
(FolderInstance.java:601)
	at 
org.openide.loaders.FolderLookup.postCreationTask
(FolderLookup.java:234)
	at 
org.openide.loaders.FolderInstance.processObjects
(FolderInstance.java:599)
	at 
org.openide.loaders.FolderInstance$Listener.finish
ed(FolderInstance.java:875)
	at 
org.openide.loaders.FolderList.createBoth
(FolderList.java:803)
	at 
org.openide.loaders.FolderList.getObjects
(FolderList.java:509)
	at 
org.openide.loaders.FolderList.access$200
(FolderList.java:50)
	at 
org.openide.loaders.FolderList$ListTask.run
(FolderList.java:877)
	at org.openide.util.Task.run
(Task.java:136)
	at 
org.openide.util.RequestProcessor$Task.run
(RequestProcessor.java:330)
[catch] at 
org.openide.util.RequestProcessor$Processor.run
(RequestProcessor.java:686)