To enable or disable Auto Complete in Microsoft Outlook 2002:
Open Microsoft Outlook 2002
Go to the Tools pull-down menu and choose Options
Click the E-Mail Options button, and then the Advanced E-mail Options button
To enable Auto Complete, check the box for Suggest names while completing the To, Cc and Bcc fields
Issue #1: Auto Complete may incorrectly remember contacts which do not exist
The file which stores frequently used contacts may become corrupt. To correct the problem, the contacts file can be reset by deleting the Microsoft Outlook "nickname list" file, which is located in Application Data\Microsoft\Outlook folder (for each Outlook profile). The file name ends in .NK2. Note: Deleting this file will remove all contacts.
Note: if you need to view the contents of the AutoComplete / nickname file then try this utility: http://www.nirsoft.net/utils/outlook_nk2_autocomplete.html
Issue #2: Auto Complete may suggest the wrong "frequently used" contact
To remove a contact from your list, "... so that it won't be suggested again, open a new message and begin typing in the address. Use the up and down arrow keys to select the address to be removed from the addresses suggested. When the address to be removed is highlighted, press the Delete key. "
Issue #3: Auto Complete May Not Function Correctly After You Upgrade from Outlook 2000 Internet Mail Only to Outlook 2002.