Here's another backtrace I got this morning from IceGridGUI when performing an updating. The program continues running just fine:

java.lang.NullPointerException
at IceGridGUI.Application.Nodes.update(Nodes.java:224 )
at IceGridGUI.Application.Root.update(Root.java:1116)
at IceGridGUI.Coordinator.applicationUpdated(Coordina tor.java:765)
at IceGridGUI.ApplicationObserverI$3.run(ApplicationO bserverI.java:140)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierar chy(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarch y(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)