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.

John,

2011 Volume 2 was released before Windows 10 was available so it wasn't tested for use on Windows 10 and it is recommended that you upgrade to a current version of the windows forms toolset if you need to support Windows 10. There were changes to Windows 10 accessibility that could be impacting the issue and it might even be reproducible in Windows 7 using accessibility tools.

Note that we also only support our toolset for three years from release so 2011 Volume 2 is no longer supported.  If you are able to provide us a sample that reproduces the exception we will be happy to look at it if it is still reproduced in the latest volume of Ultimate UI for Windows Forms.  If it is already addressed there our suggestion will be to upgrade the version that you are using.

If you aren't able to provide a sample and upgrading your application to use the latest volume of Ultimate UI for Windows Forms doesn't resolve the issue, please provide the full call stack that is repeated from the call stack as that might help us identify what might be happening.

Let me know if you have any questions with this matter.