Why does iCal often say "The server responded: 403 to operation CalDAVSetPropertyQueueableOperation." This happens on both my MacBooks running 10.7.3 and has done at least since 10.7 and with iCloud. My calendar seems to work fine from my iPhone.

This popup says "Access to account “iCloud” is not permitted." and gives the option to "Go Offline" or "Ignore" and if I ignore is seems to be fine for a while and then it comes back after a few hours. 

I also have an Exchange calendar and some subscriptions but this error always reports as being from my iCloud calendar.

Any ideas how I can fix this?
This problem appears to be caused by corrupted Calendar caches and it occurs in macOS 10.12.2 Sierra as well. 

The easiest way to get rid of this problem is to:


Quit Calendar
Open Activity Viewer and Quit "CalendarAgent"



  note, using QuickLook on any calendar item in the Finder will
  relaunch CalendarAgent which needs to be not running at step 3



Delete ~/Library/Calendars/Calendar Cache
Delete ~/Library/Calendars/Calendar Cache-shm
Delete ~/Library/Calendars/Calendar Cache-wal
Launch Calendar

                 



Calendar will read the information from the surrounding data folders and files in ~/Library/Calendars/ and recreate the caches cleanly.

If for some reason the files listed to delete re-appear before you launch Calendar, it means something is triggering the system calendar operations.  Try quitting all of your applications and starting at step 2 or logging out with the "Reopen windows when logging back in" unchecked, then logging back in.