Error message when changing an appointment.

When updating meetings, sometimes I get these messages:
"Changes to the meeting cannot be saved. The meeting has been updated by
another person. Close & reopen meeting & then make your updates." I am the
person making the changes. It will work if the only change I make is to the
date & time; but if I change any text in subject line or put explanation in
body of message, I receive the error. So far none of our IT people have been
able to figure it out. Anyone else have this problem? And if so, how did you
resolve? Thanks.
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JR