Recently my Windows CE PDA went crazy and duplicated all my appointments during a sync with my desktop. This was compounded by the fact that I have over 6 years of appointments in my outlook calendar or around 5000 appointments. I was able to resolve this with the following procedure which I figured out.
Create a new view of your calendar, and select a table view. Add the “Modified” field to the view and the set the advanced filter options to display the items modified during the time you synched your PDA. Then select the first and last appointments in the list and delete them.