I ran into this issue while at work the other day. We had a user who did something to their computer and ended up getting this error.
The solution from microsoft states it works for Outlook 2002, but I found it to work on Outlook 2003 as well.
- In Outlook, on the Tools menu, click Address Book. The error may appear when the Address Book dialog box opens.
- Click on the Tools menu, ten click Options.
- Change the option under Show this addres list first to be an addres book other than the LDAP directory.
- Under When sending mail, check names using these address lsits in the following order, move the LDAP directory to the bottom of the list by selecting it and clicking the down-arrow.
This worked a charm for me and I hope that it comes in handy for some other folks as well!
Source: http://support.microsoft.com/default.aspx?scid=kb;en-us;290034
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