I have this issue only on my PC (running Windows 10), my colleague (also on WIndows 10) has no problems with it. So it seems to be related to some settings in Windows about accessibility but we cannot find it.

The stack trace provided by Visual Studio

System.Windows.Forms.dll!System.Windows.Forms.Control.Focused.get() Unknown Non-user code. Skipped loading symbols.
Infragistics2.Win.UltraWinSchedule.v9.2.dll!Infragistics.Win.UltraWinSchedule.UltraMonthViewSingleBase.MonthViewSingleAccessibleObjectBase.GetFocused() Unknown Non-user code. Skipped loading symbols.
Infragistics2.Win.UltraWinSchedule.v9.2.dll!Infragistics.Win.UltraWinSchedule.UltraMonthViewSingleBase.MonthViewSingleAccessibleObjectBase.GetFocused() Unknown Non-user code. Skipped loading symbols.
Infragistics2.Win.UltraWinSchedule.v9.2.dll!Infragistics.Win.UltraWinSchedule.UltraMonthViewSingleBase.MonthViewSingleAccessibleObjectBase.GetFocused() Unknown Non-user code. Skipped loading symbols.
Infragistics2.Win.UltraWinSchedule.v9.2.dll!Infragistics.Win.UltraWinSchedule.UltraMonthViewSingleBase.MonthViewSingleAccessibleObjectBase.GetFocused() Unknown Non-user code. Skipped loading symbols.

…

Infragistics2.Win.UltraWinSchedule.v9.2.dll!Infragistics.Win.UltraWinSchedule.UltraMonthViewSingleBase.MonthViewSingleAccessibleObjectBase.GetFocused() Unknown Non-user code. Skipped loading symbols.
Infragistics2.Win.UltraWinSchedule.v9.2.dll!Infragistics.Win.UltraWinSchedule.UltraMonthViewSingleBase.MonthViewSingleAccessibleObjectBase.GetFocused() Unknown Non-user code. Skipped loading symbols.
The maximum number of stack frames supported by Visual Studio has been exceeded. Annotated Frame

We are running on v9.2.

Did you ever solved this problem with the latest released? I have the same issue on some Windows 10 machine but not all of them.

I have been able to avoid this Exception by disabling the AccessibleObject in a subclass of UltraMonthViewSingle.

class UltraMonthViewSingleWithoutAccessibility : Infragistics.Win.UltraWinSchedule.UltraMonthViewSingle
{
    protected override AccessibleObject CreateAccessibilityInstance()
    {
        return null;
    }
}

Then, I use this class instead of UltraMonthViewSingle.