Sporadic Java error when opening Content Explorer (6.5.2)

We’re see sporadic Java errors when opening the Content Explorer - the thermometer bar for the Content Explorer applet stays on the screen (with progress at 100%), and the Java console shows the error message pasted below.

This doesn’t happen every time we open the Content Explorer, and I can’t figure out any pattern to when it does happen. Has anyone else seen this? Any clues about what causes it?

Java console error:

Exception in thread “AWT-EventQueue-3” java.lang.NullPointerException
at com.percussion.cx.PSMainDisplayPanel.setData(Unknown Source)
at com.percussion.cx.PSMainView.valueChanged(Unknown Source)
at javax.swing.JTree.fireValueChanged(Unknown Source)
at javax.swing.JTree$TreeSelectionRedirector.valueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.fireValueChanged(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.notifyPathChange(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.setSelectionPaths(Unknown Source)
at javax.swing.tree.DefaultTreeSelectionModel.setSelectionPath(Unknown Source)
at javax.swing.JTree.setSelectionPath(Unknown Source)
at com.percussion.cx.PSNavigationTree.setSelectionPath(Unknown Source)
at com.percussion.cx.PSContentExplorerApplet$1.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)