Mac calendar app (iCal) displays error message "server responded with an error"

Solution 1:

Try following sequence.

In System Preferences, Internet Accounts, deselect all Calendars to stop the sync.

Wait for a while for the process to stop.

Than click on the "Revert to Server"

Re enable Calendars.

Solution 2:

You may need to empty your iCalendar cache. You can find detailed instructions online, but the main points are:

1. Backup your iCalendar data, particularly if you have locally stored data.
2. Delete cache files in /Users/$USER/Library/Calendars/ -- basically files with the word "Cache" in the title; there were 3 or 4 files when I did it.
3. Open iCalendar and reconnect.

Note: This persistent error seemed to start for me when I was performing a Calendar action and had a hard network failure while the action was in progress.

Solution 3:

I tried the answers posted here with no success. But seems that what have made the Calendar work again, was removing the accounts from the Internet Accounts, restarting the system, and then adding them again.

The entire process was a sum of of the answers here, plus the accounts removal. It was something like this:

1. Quit Calendar, and kill the CalendarAgent process;
2. Delete the "Cache" files from ~/Library/Calendars;
3. Go to Internet Accounts, disable everything;
4. Restart the laptop;
5. Go to Internet Accounts again, and remove all accounts;
6. Restart the laptop;
7. Go to Internet Account for the third time, and add back all your accounts;
8. Restart the laptop;
9. Hopefully Calendar will be working again as mine did and is still doing.

Note 1: Before this whole process, I also tried to delete every file from the ~/Library/Calendars, and that didn't help anything.

Note 2: all my accounts are Google accounts and I didn't backup anything. I have no iCloud or local calendars.