Missing Exchange calendar in iCal I'm getting mad here while trying to fix a issue with iCal and Exchange. 

After removing and adding back the Exchange Account in 'Setting' 'Internet accounts' the Exchange Group in the calendar has disappeared 



Mail and contacts are working fine and are in sync with exchange, but in iCal there is the exchange account missing :-(

I tried several stuff: removed and added the exchange account. Double and tripple checked that "Calendar' is activated in 'Internet Accounts' and that in the Calendar Settings the Exchange account is activated, too.

Then I have stopped iCal, removed everything from ~/Library/Calendars, gone into ~/Library/Preferences and removed everything containing iCal. 
rebooted several times (as suggested here https://discussions.apple.com/thread/7837872) .

And talked with Apple Care too but the girls were overwhelmed and couldn't help.

The same account works with calendar on my iPhone w/o any problem.

Any help is welcome, I don't want to switch to Outlook just because of this :-(

My system: MBP Retina 13'' early 2015
MacOS Sierra (10.12.2)
Calendar 9.0 (2155.15)
I had exactly the same issue and thought it might be the Accounts sqlite database file that was corrupted. So i removed the exchange account and then:

in: 
~/Library/Accounts there is:

Accounts4.sqlite
Accounts4.sqlite-wal (write ahead log file)
Accounts4.sqlite-shm (temporary file)


i did the following as another admin user on the box (to be sure no files were open). This is all on your own risk by the way!


first a backup

cd useraccount/Library/Accounts
mkdir backup
mv Accounts4.* backup/

Rebuild Accounts file:

sqlite backup/Accounts4.sqlite ".dump" | sqlite Accounts4.sqlite



Then log out and log in again on the right account
Add the exchange account again
open ical and wait some time to give ical time to sync. My account took approx. 10 minutes!