On occasions, it may be necessary to clear the data from the iPhone or iPad calendar application and do a fresh, complete sync. Use the following procedure:
From the Home screen go to Settings > Mail, Contacts, Calendars.
Select your Exchange account.
Set the option to sync the calendar to Off.
Return to the Home screen and go to the Calendar application. Verify that the calendar is empty.
Return to the Home screen and go back to Settings > Mail, Contacts, Calendars.
Select your Exchange account.
Set the option to sync calendar data to On.
Go back to the Home screen and go to the Calendar application. The calendar will re-populate with data from the server.
Note: The initial sync may take an hour or more.