Some cultures cannot convert future dates into strings. If the expiration date of an X.509 certificate is beyond the range of the culture, X509Certificate.FormatDate(DateTime) falls back to a calendar that can express the date. If the System.Globalization.CultureInfo.Calendar value is System.Globalization.UmAlQuraCalendar, the calendar is changed to the System.Globalization.HijriCalendar class; otherwise, it is changed to the System.Globalization.CultureInfo.InvariantCulture.