Using Classic Outlook on Windows for personal email, calendar, and contact management
Yup, this is some cosmetic bug that requires to be fixed, I have users report this to IT about this same issue.
The users have the new profile created, it doesn't help.
Somehow it seems only appear as cosmetic, users claim the meeting they accepted was working fine.
Just an annoying error message.
This only happens when the users manage calendars for others.