Calendar gives error for Gmail Account: 403 CalDAVAccountRefreshQueueableOperation Recently I started getting errors from Calendar.app about my synced Gmail calendars. I haven't made any changes to my Gmail security settings.
Usually if Google needs to be authenticated for macOS apps it pops up a little portal window asking me to sign in. I haven't been able to trigger this window to popup.
It seems that at least one of my calendars is still syncing between Calendar.app and Google Calendar in both directions. All calendars are on the same account.
Just in case this is relevant, I recently (2-ish weeks ago) upgraded a different mac on my apple id to Mojave.
Update:
I have cleared the iCal cache as per google support advice, as well as revoked authorization from google and re-authorized as per this recent thread on google support forum. The issue still remains.
macOS 10.10.5
 The server responded:
“403”
to operation CalDAVAccountRefreshQueueableOperation.


Google Support thread for this issue.
Apple Discussion thread for this issue.
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.
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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 &quot;CalendarAgent&quot;
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 &quot;Reopen windows when logging back in&quot; unchecked, then logging back in.
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