Apple Calendar Can't Save Event to Exchange

In this post, I’ll explain how to fix the pesky Calendar can’t save event X to Exchange Server issue with Apple’s Calendar in OS X or macOS. The issue occurs when the Mac Calendar won’t sync with Exchange and then refuses to accept the calendar data on the server.

Calendar and Exchange

Apple’s Calendar (prev. iCal) in OS X/macOS and Microsoft Exchange do not always play together nicely. At work, we have a bunch of Mac users who had issues with our on-premise Exchange 2010. When we migrated to Office 365 the situation improved dramatically, but I still ran into the occasional problem.

One of the more annoying problems is when Calendar doesn’t allow you to make changes to an event or even delete it. But instead, it responds with the following error message: “Calendar can’t save event X to Exchange Server.“

Calendar can't save to Exchange — Calendar can’t save to Exchange

The Calendar app often gives you three options: Revert to Server, Try Again and Ignore. In some cases, neither option resolves the issue, and the error message keeps coming back, every time Calendar tries to synchronize with the Exchange Server.

Note: The screenshot above is for illustrative purposes only. I triggered the error by adding a too large attachment to my test event. Your error message may look slightly different.

Related article: Mac First Aid – How to fix common Mac problems

How to fix: Calendar can’t save event X to Exchange Server

I don’t know the exact cause of this issue but I can only assume it is related to a corrupted event or individual event data Exchange doesn’t like (i.e., large attachment). If you cannot resolve the problem by any of the three options Calendar offers you, it is time to fix the problem manually.

The solution involves deleting some cache files and restarting all Calendar processes. In a nutshell, you have to:

Quit Calendar application (Command + Q)
Quit Apple Mail
Open Activity Monitor (through Spotlight or Launchpad)
Search for “Calendar” and quit all the relevant processes
Open Finder and navigate to ~/Library/Calendars
Double-check Activity Monitor to make sure no Calendar-related processes are running
Delete cache files
Relaunch Calendar

Step 1: Quit Calendar and Mail

Quitting Calendar can be done through the keyboard shortcut Command + Q or via the Calendar > Quit Calendar menu. The same steps apply to Apple Mail. It’s essential to quit Mail too because it integrates with Calendar, depending on your configuration. That integration can lead to locked files that you can’t delete or, in some cases, it immediately recreates files you want to delete.

Step 2: Open Activity Monitor

To launch Activity Monitor go through Launchpad (second icon from the right in your dock) or use Spotlight (Command + Space).

Calendar can't save event X to Exchange Server — Launching Activity Monitor through Spotlight

Apple Calendar can't save event to Exchange — Activity Monitor: Make sure you kill all relevant processes

Step 3: Quit All Calendar Processes

Quitting the Calendar application is not enough because there is still a background process running called CalendarAgent that needs to be terminated as well. The best way to do that is through Activity Monitor. Just search for all processes containing the phrase “Calendar” and quit or force quit them all. Once done, leave Activity Monitor running and make sure none of the Calendar processes magically relaunch.

Step 4: Delete Cache Files

Open Finder and navigate to ~/Library/Calendars either through the keyboard shortcut Shift + Command + G or the Go > Go to Folder… menu. There you will see up to three files starting with the name Calendar Cache. Drag all three files to the trash.

Delete Calendar cache files from hidden Library folder — Finder: ~/Library/Calendars

Step 5: Relaunch Calendar

As the last step, relaunch Calendar and don’t freak out if all your events are gone. It will take up to a few minutes to synchronize them back from the server. The cache files you deleted above-contained data from all calendar accounts, not only Exchange. Consequently, all the accounts will have to be synched. Worst case scenario, you may have to terminate all Calendar processes via Activity Monitor again (to force the re-sync) or simply restart your Mac. Rest assured, you did not lose any data!

Alternative Calendar apps

If you are fed up with Apple’s native Calendar app, you might want to give Fantastical or BusyCal a shot. I have used twice and never experienced any persistent problems like the one described above.