Setup:
Had radchartview with showtrackball = false, and a form checkbox to enable disable the trackball

So startup showtrackball = false, the start appl, all ok, mouse over chart, all ok,   then use checkbox to set showtrackball=true, then mouse over chart all ok, then use checkbox to set showtrackball = false (again) then mouse over - and get this crash!

Exception

System.NullReferenceException was unhandled
  HResult=-2147467261
  Message=Object reference not set to an instance of an object.
  Source=Telerik.WinControls.ChartView
  StackTrace:
       at Telerik.WinControls.UI.ChartTrackballController.GetPointText(DataPoint point)
       at Telerik.WinControls.UI.ChartTrackballController.GetTrackballText(List`1 points)
       at Telerik.WinControls.UI.ChartTrackballController.MoveTrackball(PointF location)
       at Telerik.WinControls.UI.ChartTrackballController.OnMouseMove(MouseEventArgs e)
       at Telerik.WinControls.UI.ChartWrapper.WrapperCallOnMouseMove(MouseEventArgs e)
       at Telerik.WinControls.UI.RadChartElement.OnMouseMove(MouseEventArgs e)
       at Telerik.WinControls.RadElement.DoMouseMove(MouseEventArgs e)
       at Telerik.WinControls.ComponentInputBehavior.SelectElementOnMouseOver(MouseEventArgs e)
       at Telerik.WinControls.ComponentInputBehavior.OnMouseMove(MouseEventArgs e)
       at Telerik.WinControls.RadControl.OnMouseMove(MouseEventArgs e)
       at System.Windows.Forms.Control.WmMouseMove(Message& m)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
       at Telerik.WinControls.RadControl.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
       at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
       at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(IntPtr dwComponentID, Int32 reason, Int32 pvLoopData)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
       at System.Windows.Forms.Application.Run(Form mainForm)
       at Elo.Rpv.WinForms.Program.Main(String[] args) in z:\00 ELECTROLOGIC.RPV\30 SW\02 Git\Rail Profile Viewer\Rail Profile Viewer 1\Elo.Rpv\Elo.Rpv.WinForms\Program.cs:line 22
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: