iCal is not allowing me to create new events

I had this problem for a while, and its been annoying me, as I depend on my iCal alot.
When I want to create a new event, a pop up menu comes up saying :
"You can’t add or change events in the Birthdays calendar."
With, "Events in the Birthdays calendar come from your contacts in Address Book. To change them or add birthdays, use Address Book." under.

I checked my preferences, but it wont allow me to uncheck the 'show birthday calender' box.

Help!?