Why does not Calendar.app sync to exchange calendar on Mac OS X?

I found these steps on the Apple site and modified them - the modifications work.

• open Calendar
• Calendar -> Accounts
• Disable exchange calendars
• Reboot

Now re-enable

• open Calendar
• Calendar -> Accounts
• Enable exchange calendars

Since I deactivated rootless in my Mac OS X, calendar.app has no problems with sync to our Exchange server.

One way I've fixed Calendar syncing problems with Exchange and/or seeing the triangle warning sign is the following two steps (as alluded to in previous answers):

1. Close Apple Calendar and Apple Mail apps
2. In a Terminal run the following (which will kill any Calendar related processes and then remove the caches):

   pkill -f Calendar
   rm ~/Library/Calendars/Calendar\ Cache*
   

Then start the Calendar and it will pop up an info dialogue box saying it's rebuilding the caches and then it should work again..