I’ve had a few users with this error this month, so here is a fix. The problem: when you open Calendar on your Mac, you are quickly greeted with a window saying, “Couldn’t move your calendars to iCloud because an error occurred”. It will keep coming back, whatever you choose to do, and it makes the Calendar app useless.
I don’t know what the precise cause is – it affects different versions of Mac OS, so it is not system specific. And so the fix is a bit of a blunt instrument, though hopefully without causing any lasting collateral damage.
- Open System Preferences, go into your iCloud settings and turn-off Calendar sync.
- Switch to the Finder, select the Go menu with the Option key held down on your keyboard – you will see a menu item called Library appear. Choose Library and find the two folders, Caches and Calendars. Open each folder and select all items (CMD-A on your keyboard) and then delete (CMD-Backspace) everything in the two folders.
- Then restart your Mac and log back in.
- Go back to System Preferences, iCloud, and enable Calendar again.
- Then you can open the Calendar app again. Hopefully the error message has gone. And also your calendar items will return via iCloud after a few moments.
Obviously, do the above with care, be sure you have a Time Machine backup, and proceed at your own risk.