Read the statement by Michael Teeuw here.
iCal calendar problem. Is it just me?
I’m having trouble using an iCal calendar feed. It used to work, but stopped a few days ago. Is any of you successfully using an iCal feed at the moment?
Never mind. I created a new calendar and use the new url. Problem solved.
I´m having issues as well. Testing the URL the browser ask for an authorization.
Did apple tinker on the server-side? (alongside the ios10/sierra release?)
Maybe. I just created a new agenda with a new URL and that solved the issue.
I had the same problem. I removed the calendar url, rebooted, then added the calendar url back in and rebooted again.
It seems to be working now.