An error occurred when writing to the calendar Verjaardagen! Please see below for more information. If you're seeing this message after snoozing or dismissing a reminder and this is for a calendar you do not want to add or edit events for, you can mark this calendar as read-only to avoid such experience in future. To do so, get to the calendar properties by right-clicking on this calendar in the list in the calendar or task view. The calendar is marked as read-only because it contains birthday's and reminders cannot be dismissed. What is the proper way handle a anniversary calender and reminders?