One day both my Exchange calendar and Google Calendar stopped syncing with iCal (Mountain Lion's Calendar application). No error message or whatsoever was displayed; remotely created events just didn't show up in the Calendar application.
I've tried deleting and readding the accounts and even completely deleting the Calendar app's settings:
sudo rm -Rf ~/Library/Calendars/* sudo rm -Rf ~/Library/Caches/com.apple.iCal sudo rm ~/Library/Preferences/com.apple.iCal.plist
After adding my Google Calendar account, I get an empty "Google" calendar group with no actual calendar inside:
The very same is happening if I add an Exchange account. However, on my iPhone all calendars work just fine.