NullReferenceException - Edit Template

Hi,
I'm gettings NullReferenceException when I'm clicking in Blend on the Control -> Edit Template -> Edit a Copy.

   at Telerik.UI.Xaml.Controls.Input.DateTimePicker.GetSelectorWidth(Boolean clampToWindow)
   at Telerik.UI.Xaml.Controls.Input.DateTimePicker.MeasureOverride(Size availableSize)
   at Windows.UI.Xaml.UIElement.UpdateLayout()
   at Microsoft.Expression.WindowsXamlPlatform.Views.WindowsUIXamlImageHost.WindowsXamlSceneWrapper.UpdateLayout()
   at Microsoft.Expression.WindowsXamlPlatform.Views.WindowsUIXamlImageHost.set_RootInstance(Object value)