Q: caldavwriteentityqueueableoperation 403

iCal on OS X Yosemite, I'm receiving this error message when trying to add an event to iCloud calendar:  caldavwriteentityqueueableoperation 403 - when trying to add from Safari or Mail.  I can add through an exchange calendar, but not on my iCloud, which is what is needed.

Does anyone have a fix?

Suggestion? 

Hint?

Thanks!