Currently Being ModeratedOct 10, 2012 1:46 PM (in response to K1200-GT)
I had this same problem and drillbitmarketer's solution worked for me.
In the Calendar application, open preferences and remove your Exchange account. Open System Preferences and open Mail, Contacts, & Calendars. There I had two Exchange accounts. Remove the inactive one and enable Calendars & Reminders on the remaining account.