If you use System Preferences > Mail, Contacts & Calendars to add your gmail account, and enable Mail, Calendar & Reminders, Messages and Notes, your caldav account for calendar will be set up with a username like <your username>@
gmail.com, originating a caldav url like:
This is an invalid url, as google is expecting only your username and not username and domain.
If you delete your GMAIL account from Mail, Contacts & Calendar and go to Calendars > preferences > accounts and choose add an account, choosing account type caldav, and entering only your user name (without domain), password and your caldav url in the following format https://www.google.com/calendar/dav/<your username>@gmail.com/user your account is setup correctly and no errors will appear on console log.
Furthermore, if you wish to re-enable mail, Messages and Notes, just head up to System Preferences > Mail, Contacts & Calendars, choose your recently created gmail account and enable those checkboxes.
This solved my 4000+ error messages per day on console log for CalendarAgent.
If you have multiple calendars on the same account, go to https://www.google.com/calendar/syncselect and select those that you want to show on calendar.
p.s. this must be an osx implementation error that forces your username to be suffixed with @gmail.com when you register a gmail account through System Preferences > Mail, Contacts & Calendars.
If you use calendar to add the same account, the suffix is not appended to your username and all is solved.
Hope this help the rest of us, even those that have not yet detected this issue.
