I am the delegate of my manager. I set up a meeting from her calender with
another member of staff. Everything is fine and the meeting is accepted. I
then need to change the meeting to a different time and I receive the
following error:

"The item could not be saved because it has been changed by another person.
Do you want to save a copy in your default Calender folder? If you click Yes,
you need to copy and paste your changes from the "copy of" item in your
default folder into a new update for this meeting."

There have been no changes by my manager, myself of the meeting respondee
other than their acceptance of the meeting, so any idea why I get this
message?