I am adding some links to some great information that may offer you
a solution:
This article describes issues that may occur with meeting information if you
use Microsoft Outlook or Microsoft Outlook Web Access in an organization
that is using Microsoft Exchange Server.
http://support.microsoft.com/default.aspx?scid=kb;en-us;899704&sd=rss&spid=1773
Microsoft Office Online: Outlook meeting requests: Essential do's and don'ts
http://office.microsoft.com/en-us/help/HA011276781033.aspx
Calendar items disappear from user's folders
http://support.microsoft.com/kb/299046
301234 Calendaring Agent fails with error code 0x80040229 when
you save appointments
817954 You receive no warnings when a meeting is overwritten
in your Outlook 2003 Calendar
824097 A meeting is canceled after you receive both a meeting
update and a meeting cancellation in Outlook 2003
890436 How to troubleshoot missing and duplicate appointments
in Outlook
886688 Recurring appointment that is associated with a meeting
request may be removed from a recipient's calendar
222388 Meeting cancellation and update messages sent to wrong
attendees in Outlook
821695 Invitations are not sent to attendees who are added through
Meeting Workspace in Outlook 2003
822586 Users are not added to the attendee list of a recurring
meeting in Outlook
281524 The delegate copy of a meeting request is sent to the
Deleted Items folder
828493 FIX: After you accept a meeting request in through a remotely
synchronizing mobile device, the folder containing the meeting request
may be deleted
Nikki