Say you want to delete an item scheduled for Dec 21, 2005 from the first (recurrent) event in a schedule. Assuming the variable 'calendar' identifies a Planner.NET control with a recurring item in
its schedule:

Item item = calendar.Schedule.Items[0];
ItemCollection items = item.Recurrence.GenerateItems(
  new DateTime(2005, 12, 21),
  new DateTime(2005, 12, 21));

if (items.Count > 0)
  item.Recurrence.MarkException(items[0], true);
calendar.Invalidate();
 

That's what happens internally when a user deletes an item from recurrent series. The control uses GenerateItems to display items in the currently visible time range, and if one of the generated items is deleted, it is marked as an exception of the recurrence.

Hope this helps,
Stoyan