Q: How do I delete duplicate birthdays in my iCal?

For some reason all the birthdays are showing up twice in my iCal.  I can't click on either of them to delete.  Instead it refers me to the Address Book where the information is listed only once.  How can remove one of the instances?  I've tried to remove the calendar from the subscription and it removes both instances but when I add it back, it adds two entries.  Thanks for any help!