It is important that you maintain the latest updates for Outlook 2000. This
is especially true when working with Exchange 2003 since there would be
updates to Outlook 2000 to provide smooth functionality with Exchange 2003.
I checked for any known issues like you describe.
OL2000: (CW) Error Message "The Operation Failed" When Forcing Replies
WGID:220
ID: 223897.KB.EN-US
http://support.microsoft.com/?id=223897
You also want to discover if this is a problem with Outlook or the mailbox.
You can do this by having the user access their mailbox from another system
that they have never logged onto.
If the problem follows the user then it could be a problem with the
mailbox.
If you discover this is a problem with the mailbox then you will need to
export the data from the mailbox using Exmerge utility, delete the mailbox,
recreate the mailbox and then test first before importing the data to
ensure things are functioning properly.
Once you have determined the problem is corrected then import the data to
the mailbox using Exmerge.
HOW TO: Recover or Restore a Single Mailbox in Exchange Server 2003 WGID:489
ID: 823176.KB.EN-US
http://support.microsoft.com/?id=823176
Tammy