The server responded: “403” to operation CalDAVWriteEntityQueueableOperation.

Please take each of the following steps that you haven't already tried. Stop when the problem is resolved. Back up all data before making any changes.

Step 1

In the Internet Accounts preference pane, delete any calendar accounts you don't use.

If there's no improvement, delete all calendar accounts and add them back. With an iCloud account, all you have to do is uncheck and recheck the box marked Calendars & Reminders in the iCloud preference pane.

Step 2

You may be trying to access an invited event that you declined, or one that was rescheduled after you accepted it. The error message should give you a clue as to what it is. If the calendar is on iCloud, you can bring up the Calendar on the website and select

Show Declined Events

from the popup menu with the gear icon in the upper right corner of the page. The declined events will appear in gray, and one of them should match what's shown the error message. [Credit for this solution to ASC member Psi.]

Step 3

If you get the error when trying to accept an invitation in an email attachment, it's because the organizer didn't properly create the event.

Step 4

Follow the instructions in this support article. Modify as necessary for a calendar that's not on iCloud.

Thank you, this was most helpful to me, specifically Step 2. I went ti iCloud on the net, clicked on "Show Declined Events" and deleted them all. Voila! The issue disappeared.. (kinda like the money in mortgage-backed securities.. now, let me laugh all the way to the bank)

p.s: Thank you again!

Linc, this solved the endless 403 message problem for me. Step 1b seemed to do the trick. However, Step 1a wasn't clear to me: I couldn't locate an Internet Accounts pane exactly, and I wasn't sure if this was in System Preferences, Calendar preferences, or where.

Thanks very much!

No. 2 is a life-saver. I hadn't seen this tip before. Eliminated my problem completely🙂