OS X Mountain Lion Calendar Exchange Sync Problems – A Fix



Update: Well, the issues have returned for me after just a few days. Looks like this wasn’t a fix after all. So, consider the post notice that there’s a real problem with syncing the Calendar with an Exchange server, at least for some folks.

If you’re like me, you’ve experienced some issues with the Calendar app synchronizing with an Exchange server. You might also have some issues with the Reminders app keeping in sync as well.

For me, the problem manifested itself most often with the following error:

Calendar can’t save the event “Item title” to the Exchange server.

The account “Exchange” currently can’t be modified. To discard your changes and continue using the version of your calendars that’s on the server, click Revert to Server.

The options on the dialog box are:

  • Revert to Server
  • Try Again
  • Ignore

Calendar items and reminders would sync eventually in most cases, but the error would pop up apparently randomly. It was driving me batty.

Fortunately, the fix seems to be pretty straightforward, and the hat tip goes to a member of the Apple support community. In this thread, the member furyg3 outlines the steps to resolve the issue:

    • Open Calendar (formerly iCal).
    • Go to the Calendar menu and select Preferences.
    • Select the Accounts tab.
    • Remove the Exchange server account which is giving you the error messages. This calendar will be removed from the Calendar app.
    • Go to System Preferences and click on the “Mail, Contacts & Calendars” pane, find your Exchange server account, and check the “Calendars & Reminders” option to re-enable your calendar.

This is working for me. Give it a try, and if it works for you let me know in the comments.



  1. yep. worked

  2. William Cerniuk says

    I have found that deleting the calendar cache file will cause the calendar app to re-import the calendar data from disk. This solves the problem for a little while.

    ~/Library/Calendars/Calendar Cache

    Also believe that Mail is manipulating this file and could be the culprit behind the problems.

    • mark.coppock says

      Interesting. I’ll give that a try. If Mail is doing something, then I don’t think there’s anything we can do about that, but it’s certainly an intriguing idea.

  3. William Cerniuk says

    Your solution seems to be holding up better than simply deleting the cache. So far, today, it is working all day instead of craping out several times a day as normal.

  4. William Cerniuk says

    Ok, day 2, symptoms still clear. Very optimistic after the plague of errors in Calendar.

    I found this page by a google search that matched the example text below your statement “problem manifested itself most often”. Big thanks for posting exactly what the calendar dialog displayed.

  5. I tried the delete and re-instate route, but once re-instated the same message came up. Is Apple on the case does anyone know.

  6. Alas this fix is only short termed, as the problem eventually come back after a few weeks 🙁

  7. jack mangan says

    It worked for me! Many thanks. The iCal revert to server message was like the Zombie that would not die.

  8. This has worked for me – has synced all the appts that had been missed. Will see how it goes over the next days/week.

  9. Hi all,
    until two weeks ago I struggled with the same problem. I tried all what is mentioned above, but without success. But what does help (at least since two weeks now): I removed the complete exchange account via System Preferences -> Mail, Contacts & Calendar and then (re-)add it there again. Everything (Mail, Contacts and Calendar) worked immediately again until now.
    Maybe this can be helpful for others, too.
    PS: I will give an update if it fails again.

    • mark.coppock says

      Stephan – Thanks, but I believe some folks have already tried that. I lost some comments after a hack, but removing-re-adding the Exchange account only helps for a limited time. Good luck, though–if it works for you, more power to you. 🙂

  10. So far so good. Day one going strong. I removed the cache as recommended by William Cerniuk

  11. Wm. Cerniuk says

    The removal of that cache file seem to be the only way to clear the problem up although signs point to Mail actually causing the problem.

    I confirmed that Mail edited the file. I watched the file access of Mail to the cache file repeatedly. Then I quit the apps, deleted the cache and ran Calendar to repair/rebuild. I confirmed that it was working by posting a calendar event to exchange, no errors. I quit and re-launched Calendar, no problem. Then I quit calendar and intentionally did not run it for the next 4 hours

    Next I launched and ran Mail for the next 1/2 of the day leaving Calendar alone and using my iPhone only to keep my appointments. I received several invites in Mail / Exchange account ones and standard ics ones. 4 hours later I launched Calendar and sure enough, Calendar was broken again with the same abort-retry-flail message.

    Unless Calendar spontaneously broke the cache file the moment it was launched, the Mail access to the cache file in the prior 4 hours broke the cache file while Calendar was not running.

    So pulling from my last post, I am relegated to deleting and recreating the Calendar cache file multiple times a day now at:
    ~/Library/Calendars/Calendar Cache

    but things do tend to work for a while afterwords. Still don’t know exactly how to trigger the problem.

  12. Great, worked pretty well! Thank you

  13. To Mr. Curniuk,

    Did you also try the other fix out there regarding time zones? I thought the time zone thing would help us but found that we aleady the suggested settings.

  14. Jason Miller says

    Are you guys only using iCal to create/edit meetings, or do you also edit them with Outlook or another client? I have most problems with calendar events with no invitees (placed there to book my time, primarily), both timed events and all-day events.

  15. I deleted the cache file and my accounts in Calendar and recreated the accounts in general > preferences. Unfortunately the “can’t save” error returned after a week. The accounts also reappeared in Calendar settings. Is this normal?

  16. Worked for me! Thank you!

  17. The error message was driving me crazy, I tried to log into the calendar via webmail thinking that it would have the event that couldn’t be deleted – but it didn’t. This solution worked for me.

    I suspect I will have to do it every once in awhile – some Calendar bug that hasn’t been fixed.

    But it’s easy to do and it didn’t take long for my Calendars to resync.

  18. Thank you. This worked beautifully.

  19. This really is actually fascinating, That you are a quite specialist blogger. Ive joined your rss feed and sit up for looking for more of your excellent post. Also, I have shared your web site in my social networks!

  20. Peter Galloway says

    The cache delete didn’t work for me, but completely deleting the Exchange account, deleting the cache, and then re-establishing the Exchange account worked for me (well, 4 hours all good so far).

    [mavericks / Calendar / Exchange]

  21. Mathew Webb says

    I was having a bit of a different problem where my meetings were not showing up in the calendar app at all. I went into the account preferences as stated and just unchecked calendar as I did not want to lose all my mail etc…. I then closed the calendar app, re-opened. I then re-added calendar under accounts and then all my meetings popped up.

    Thanks again!


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