How do I fix 'an error has prevented iCloud Calendar from working properly' on Mac?

my icloud calendar won't load and keeps saying "an error has prevented this application from working properly" this happens routinely - and then occasionally it will load and my calendar appears - but then often it won't work to add events saying an error occured. I've tryed reloading - closing and reopening - and restarting the computer - all works occasionally but mostly doesn't. I also send the error reports to APPLE each time it requests.

[Re-Titled by Moderator]

Original Title: iCloud Calendar won