.NET Framework error when renaming a terrain model

As I was renaming a terrain model, this nonfatal error came up. After clicking Continue, everything seems to be working normally.

System.NullReferenceException: Object reference not set to an instance of an object.
   at Bentley.DTM.Element.DTMNavElement.GetPropertyList(NavigatorNode nodeIn)
   at Bentley.DesignExplorer.NavigatorPropertyGrid.ReloadInstanceList(List`1 navigatorNodesIn)
   at Bentley.DesignExplorer.NavigatorPropertyGrid.Reload()
   at Bentley.DesignExplorer.NavigatorPropertyGrid.OnReloadTimeout(Object senderIn, EventArgs eventArgsIn)
   at System.Windows.Forms.Timer.OnTick(EventArgs e)
   at System.Windows.Forms.Timer.TimerNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

Geopak SS3 .722.