I use my Outlook.com calendar and have for years. When I clicked Edit Event in the popup, it brought up my niece’s birthday recurring event from the birthday calendar on Outlook.com. I’ve had this in my calendar, again for years. Why would this event be causing an error suddenly?
I changed an item in the event just to see if that would rewrite it and fix it, nope. So I then deleted it using eM Client and recreated it, after clicking save and close, boom same error. I went on outlook.com and deleted the event an added it there, now it wouldn’t show in eM Client.
Finally I just added it to my main calendar on outlook.com. No problems. Again, I’ve had this calendar and in particular her b-day event for probably 25-26 years (this account is a Hotmail account, it is so old, I created it as a beta tester for Hotmail in the 90s I don’t remember when the calendar was added to hotmail back in the day). Confirmed grey-beard.