Recurring Appt in Public Folder

Have a user who modifies a Recurring Appt. in an Exchange
Public Folder. They do a save and close. When they try
to open the appt again, they receive a message that
Outlook cannot read one instance of the recurring appt.
The data that they changed previously is gone. They close
out of Outlook and open the appointment again and they do
not receive the message. It appears as if when they choose
save and close, an Outlook Process is not being closed
properly. No one else is having this problem and can save
and edit recurring appts. in the Public Folder Calendar.
Anyone seen this before or have a place where I can find
the info for the fix?