I don't quite understand your response.
This is affecting both in-house staff and outside appointments. There have been no changes to the email addresses for any of these people.
It is selective as to when it happens and it is not only on my calendar; it is for several of the Executive Assistants when we are trying to update existing appointments - either by changing the date, time, or cancelling them.
It is also selective in that it does this on some appointments but not on others, and it's even doing it on reminders that I've set up.
I tried your suggestion - I removed the person from the calendar invite, put their email address back in and tried to cancel the appointment. I got the same response - Outlook would not perform the action because of parameter settings.
I have no idea if our IT department restarted the server. We don't have the best IT support here.
I will send them a helpdesk request to do this, as well as copy them on this conversation.
Thank you for your assistance.