If you have two or more calendar folders which you need to combine into one, move the items, instead of using Import.
If necessary, open the message stores using File, Open, Outlook Data file, then switch to the By Category view and select the appointment and events then right-click and choose Move to folder. You could also select and drag to the other folder or right-click and drag.
If you move, rather than copy, the message IDs won't change and any associations with contacts or other items won't be broken.
Published October 13, 2003. Last updated on May 16, 2011.