Causing exception when clicking on ribbon button

Hi,

I am using ribbon in my application, but when i am clicking on a ribbon button say tool, some time i am getting a runtime unhandeled exception, which causing application crash.

and this problem is not coming always so it unpredictable for us, so we are not able to resolve.

Following is the stack trace for the same.

DateTime: 12/9/2008 5:42:13 PM
Exception: Object reference not set to an instance of an object.
Stack Trace: at m.b(RibbonWindow A_0)
at ActiproSoftware.Windows.Controls.Ribbon.RibbonWindow.c(Boolean A_0)
at ActiproSoftware.Windows.Controls.Ribbon.RibbonWindow.OnSourceInitialized(EventArgs e)
at System.Windows.Window.CreateSourceWindowImpl()
at System.Windows.Window.SafeCreateWindow()
at System.Windows.Window.ShowHelper(Object booleanBox)
at System.Windows.Window.Show()
at System.Windows.Window.ShowDialog()
at DomainManagerGUI.DomainGUI.cmdOptions_Executed(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.Input.CommandBinding.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.Input.CommandManager.ExecuteCommandBinding(Object sender, ExecutedRoutedEventArgs e, CommandBinding commandBinding)
at System.Windows.Input.CommandManager.FindCommandBinding(CommandBindingCollection commandBindings, Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
at System.Windows.Input.CommandManager.FindCommandBinding(Object sender, RoutedEventArgs e, ICommand command, Boolean execute)
at System.Windows.Input.CommandManager.OnExecuted(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.UIElement.OnExecutedThunk(Object sender, ExecutedRoutedEventArgs e)
at System.Windows.Input.ExecutedRoutedEventArgs.InvokeEventHandler(Delegate genericHandler, Object target)
at System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
at System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
at System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
at System.Windows.UIElement.RaiseEventImpl(RoutedEventArgs args)
at System.Windows.UIElement.RaiseEvent(RoutedEventArgs args, Boolean trusted)
at System.Windows.Input.RoutedCommand.ExecuteImpl(Object parameter, IInputElement target, Boolean userInitiated)
at System.Windows.Input.RoutedCommand.Execute(Object parameter, IInputElement target)
at ActiproSoftware.Windows.Controls.Ribbon.Input.RibbonCommand.a(ICommandSource A_0)
at ActiproSoftware.Windows.Controls.Ribbon.Controls.Primitives.ControlBase.OnClick(ExecuteRoutedEventArgs e)
at ActiproSoftware.Windows.Controls.Ribbon.Controls.Primitives.ButtonBase.OnClick(ExecuteRoutedEventArgs e)
at ActiproSoftware.Windows.Controls.Ribbon.Controls.Primitives.ControlBase.a.a(Object A_0)
at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter)
at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler)
Exception Source: ActiproSoftware.Ribbon.Wpf30
InnerException:
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Thanks in advance.

Regards
Manoj Shukla