You want to remove and add (reinstall) the Outlook Address Book. It is most likely corrupted. There
are different steps depending on which version of Outlook you have:

Outlook 97
191367.KB.EN-US OL97: ErrMsg: The Address List Could Not Be Displayed
http://support.microsoft.com/default.aspx?scid=KB;EN-US;191367

Outlook 98/2000: How to reinstall the Outlook Address Book Service
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1. On the Tools menu, click Services.
2. Confirm that the Outlook Address Book service is in the list of available information services.
3. Remove the Outlook Address Book service and then restart Outlook and try to access your
contacts from the "To:" line.
4. If it is not listed, click Add, click to select the Outlook Address Book from the list of available services
and, then click OK.) Then restart Outlook and try to access your contacts from the "To:" line.

Outlook 2002/2003
319901.KB.EN-US OL: Error if You Use Your Contacts to Address a New Message
http://support.microsoft.com/default.aspx?scid=KB;EN-US;319901

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not be opened, it may have been moved or deleted, or you do not have permissions.  For information
on how to remove this folder from the Outlook Address Book, see Microsoft Outlook Help."  I have had
to create a subfolder in the Contacts folder called Address Book in order to be able to access the
feature of being able to click on the "To...." button as a get-a-round.  Any thoughts or suggestions on
this problem?

William R. Tatum III - MCSE, MCSA
Partner Technical Lead - Outlook/Office Setup
Microsoft Tecnnical Support
for Platforms and Business Applications