iCloud on PC Calendar Error: The item cannot be saved to this folder

I am using Outlook 2013 (desktop)with calendar and contacts synced to iCloud so that I can access all from my iphone. Occasionally, when I try to delete a calendar event from Outlook, I get the following error message:

"The item cannot be saved to this folder. The folder was deleted or moved, or you do not permission. Do you want to save a copy of it in the default folder for the item?"

The calendar item is NO LONGER on my iphone, just in Outlook Desktop. The item cannot be deleted or moved.

This is definitely not a permissions issue since it doesn't affect most of my calendar items, whether created on my iphone or in Outlook Desktop.

It doesn't matter if the Calendar event has a start/stop time or is all day.

Ideas on how to fix this intermittent problem, please?