Could you provide additional information please? Like steps you did before this exception appeared, your NB build
number, JDK version, etc...

Exception throws seldom on NB5.5+Java1.5 during intensive tree working (scrolling/expanding/collapsing) and parallel
tree updating. Component is C/C++ class view in CND pack.
Since I use NB5.5+Java1.6 exception do not reproduced.

Exception was repeated once:
-------------------------------------------------------------------------------
>Log Session: Thursday, July 26, 2007 8:57:25 PM MSD
>System Info:
  Product Version         = NetBeans Platform Dev (Build 070318)
  Operating System        = Windows XP version 5.1 running on x86
  Java; VM; Vendor; Home  = 1.6.0_01; Java HotSpot(TM) Server VM 1.6.0_01-b06; Sun Microsystems Inc.; D:\Program
Files\Java\jdk1.6.0_01\jre
  System Locale; Encoding = ru_RU; Cp1251
  Home Dir.; Current Dir. = C:\Documents and Settings\Alex; D:\tec\src\cnd\suite
  Installation; User Dir. =
D:\tec\src\cnd\suite\build\cluster;D:\tec\netbeans-5.5.1\harness;D:\tec\netbeans-5.5.1\ide7;D:\tec\netbeans-5.5.1\nb5.5;D:\tec\netbeans-5.5.1\platform6;
D:\tec\src\cnd\suite\build\testuserdir
  Boot & Ext. Classpath   = D:\Program Files\Java\jdk1.6.0_01\jre\lib\resources.jar;D:\Program
Files\Java\jdk1.6.0_01\jre\lib\rt.jar;D:\Program Files\Java\jdk1.6.0_01\jre\lib\sunrsasign.jar;D:\Program
Files\Java\jdk1.6.0_01\jre\lib\jsse.jar;D:\Program Files\Java\jdk1.6.0_01\jre\lib\jce.jar;D:\Program
Files\Java\jdk1.6.0_01\jre\lib\charsets.jar;D:\Program Files\Java\jdk1.6.0_01\jre\classes;D:\Program
Files\Java\jdk1.6.0_01\jre\lib\ext\dnsns.jar;D:\Program Files\Java\jdk1.6.0_01\jre\lib\ext\localedata.jar;D:\Program
Files\Java\jdk1.6.0_01\jre\lib\ext\sunjce_provider.jar;D:\Program
Files\Java\jdk1.6.0_01\jre\lib\ext\sunmscapi.jar;D:\Program Files\Java\jdk1.6.0_01\jre\lib\ext\sunpkcs11.jar
  Application Classpath   =
D:\tec\netbeans-5.5.1\platform6\lib\boot.jar;D:\tec\netbeans-5.5.1\platform6\lib\org-openide-modules.jar;D:\tec\netbeans-5.5.1\platform6\lib\org-openide-util.jar;D:\Program
Files\Java\jdk1.6.0_01\lib\dt.jar;D:\Program Files\Java\jdk1.6.0_01\lib\tools.jar
  Startup Classpath       =
D:\tec\netbeans-5.5.1\platform6\core\core.jar;D:\tec\netbeans-5.5.1\platform6\core\org-openide-filesystems.jar;D:\tec\netbeans-5.5.1\ide7\core\org-netbeans-modules-utilities-cli.jar;D:\tec\netbeans-5.5.1\nb5.5\core\org-netbeans-upgrader.jar;D:\tec\netbeans-5.5.1\nb5.5\core\locale\core_nb.jar
-------------------------------------------------------------------------------
Step before exception:
- open medium C/C++ project (I used open source project mySQL)
- at parsing time (status bar in "Progress") expand project node in class wiew
- wait content in class view
- do any action on class view or other tree-view (status bar should be in progress- it mean that class view intensive
updated)
- exceptions occurred when popup menu in project view was invoked
-------------------------------------------------------------------------------
*********** Exception occurred ************ at 8:48 PM on Jul 26, 2007
java.lang.ArrayIndexOutOfBoundsException: 4533 >= 4533
        at java.util.Vector.elementAt(Vector.java:427)
        at javax.swing.tree.DefaultMutableTreeNode.getChildAt(DefaultMutableTreeNode.java:230)
        at javax.swing.tree.VariableHeightLayoutCache.treeNodesRemoved(VariableHeightLayoutCache.java:543)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.treeNodesRemoved(BasicTreeUI.java:3805)
        at javax.swing.tree.DefaultTreeModel.fireTreeNodesRemoved(DefaultTreeModel.java:530)
        at javax.swing.tree.DefaultTreeModel.nodesWereRemoved(DefaultTreeModel.java:310)
        at org.openide.explorer.view.NodeTreeModel$Listener.removed(NodeTreeModel.java:178)
        at org.openide.explorer.view.VisualizerChildren.removed(VisualizerChildren.java:143)
        at org.openide.explorer.view.VisualizerEvent$Removed.run(VisualizerEvent.java:123)
        at org.openide.util.Mutex.readAccess(Mutex.java:293)
        at org.openide.explorer.view.VisualizerNode$QP.run(VisualizerNode.java:645)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
[catch] at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
*********** Exception occurred ************ at 8:48 PM on Jul 26, 2007
java.util.NoSuchElementException
        at java.util.LinkedList$ListItr.next(LinkedList.java:698)
        at org.openide.explorer.view.VisualizerChildren.added(VisualizerChildren.java:67)
        at org.openide.explorer.view.VisualizerEvent$Added.run(VisualizerEvent.java:87)
        at org.openide.util.Mutex.readAccess(Mutex.java:293)
        at org.openide.explorer.view.VisualizerNode$QP.run(VisualizerNode.java:645)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
[catch] at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
*********** Exception occurred ************ at 8:48 PM on Jul 26, 2007
java.lang.ArrayIndexOutOfBoundsException: 4601 >= 4532
        at java.util.Vector.elementAt(Vector.java:427)
        at javax.swing.tree.DefaultMutableTreeNode.getChildAt(DefaultMutableTreeNode.java:230)
        at javax.swing.tree.VariableHeightLayoutCache.treeNodesChanged(VariableHeightLayoutCache.java:412)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.treeNodesChanged(BasicTreeUI.java:3754)
        at javax.swing.tree.DefaultTreeModel.fireTreeNodesChanged(DefaultTreeModel.java:468)
        at javax.swing.tree.DefaultTreeModel.nodesChanged(DefaultTreeModel.java:330)
        at javax.swing.tree.DefaultTreeModel.nodeChanged(DefaultTreeModel.java:261)
        at org.openide.explorer.view.NodeTreeModel$Listener.update(NodeTreeModel.java:203)
        at org.openide.explorer.view.VisualizerNode.run(VisualizerNode.java:451)
        at org.openide.util.Mutex.readAccess(Mutex.java:293)
        at org.openide.explorer.view.VisualizerNode.run(VisualizerNode.java:430)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
[catch] at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)
*********** Exception occurred ************ at 8:48 PM on Jul 26, 2007
java.lang.ArrayIndexOutOfBoundsException: 4601 >= 4532
        at java.util.Vector.elementAt(Vector.java:427)
        at javax.swing.tree.DefaultMutableTreeNode.getChildAt(DefaultMutableTreeNode.java:230)
        at javax.swing.tree.VariableHeightLayoutCache.treeNodesChanged(VariableHeightLayoutCache.java:412)
        at javax.swing.plaf.basic.BasicTreeUI$Handler.treeNodesChanged(BasicTreeUI.java:3754)
        at javax.swing.tree.DefaultTreeModel.fireTreeNodesChanged(DefaultTreeModel.java:468)
        at javax.swing.tree.DefaultTreeModel.nodesChanged(DefaultTreeModel.java:330)
        at javax.swing.tree.DefaultTreeModel.nodeChanged(DefaultTreeModel.java:261)
        at org.openide.explorer.view.NodeTreeModel$Listener.update(NodeTreeModel.java:203)
        at org.openide.explorer.view.VisualizerNode.run(VisualizerNode.java:451)
        at org.openide.util.Mutex.readAccess(Mutex.java:293)
        at org.openide.explorer.view.VisualizerNode.run(VisualizerNode.java:430)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
[catch] at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

Reassigning to "cnd" for further evaluation...

not repeatable now.