Reset Outlook Sync Services
In some cases the Outlook Sync Services setting that controls the sync with the Apple apps (Address Book/Contacts, iCal/Calendar) may need to be reset in case the sync is set to the wrong or a missing "Outlook Database Identity". This can occur after setting up multiple email accounts in Outlook or removing one.
Follow these steps to reset Outlook Sync Services settings to restore the sync between Outlook and the Apple apps.
1. Open Finder
2. Select Go from the menu bar
3. Hold down Option/Alt and select "Library" from the menu
4. Open the Preferences folder
5. Delete these 2 files:
com.microsoft.Outlook.SyncServicesPreferences.plist
com.microsoft.SyncservicesAgent.plist
6. Open the Preferences/Microsoft/Office 2011 folder
7. Delete this file:
OfficeSync Prefs
8. Completely Exit and Re-open Outlook
9. Setup the Outlook Sync Services under Preferences.