iCal can't add event invitations to iCloud calendars When someone sends me an iCal event invitation over email, I can't seem to properly add it to a calendar I'm storing on iCloud and accessing via CalDAV. 

After accepting the invite, I get the error "https://p06-caldav.icloud.com:443/150624888/principal/ is not a location that supports this request." and I must choose "Revert" or "Go to server..". Sometimes, hitting "Revert" will keep the event in my calendar until the next update, when it will vanish. Hitting "Go to server" will immediately remove the event from my calendar and act like I never saw the event invitation in my email. 

If I try to duplicate the event and store it on my mac instead of on iCloud, iCal thinks that I've created a new event and proceeds to email everyone who was invited. 

Quite annoying, and embarrassing. Anyone know a fix?
Apple discussion boards point to a name collision between calendar or reminder lists:

https://discussions.apple.com/thread/3384144

Try deleting or renaming the Reminder list on icloud.com (after backing up reminders)