Calendar gives error for Gmail Account: 403 CalDAVAccountRefreshQueueableOperation

I'm having the same problem. I'm also operating Yosemite (10.10.5)

Saw the solution below for Sierra elsewhere, but it didn't work for me.

+++++++++

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.

++++++++