Q: Calendar error: https//... not a location that supports this request

I get the following error in Calendar:

https://p33-caldav.icloud.com/205584027/principal/ is not a location that supports this request.

This comes up when I open Calendar, or if I refresh Calendar.  I cannot figure out which calendar this applies to or how to get additional information on what is causing this error. 

I run a MacBook Pro and share the calendar on my iPhone.  So far, I have no problems with sharing data between the two devices or to the cloud version of iCloud. 

Any suggestions would be appreciated.

Confused in North Carolina.