This is a common occurrence when moving things around -- the association
between the Contacts folder and the Outlook Address Book gets broken.  To fix
it, go to Tools | E-mail accounts, select "View or change existing
directories or address books", and click Next.  If you don't see the OAB in
the Directories and Address Books list, click the Back button, then select
"Add a new directory or address book", then "Additional Address Books", and
add the OAB.  Then keep clicking Back until you get back to the first dialog
box, and go back to the Directories and Address Books list as you did earlier.

Once the OAB appears in the list, select it and then click Change to make
sure the Contacts folder(s) you want to display are listed.  If any of them
aren't listed, you'll need to enable those Contacts folders as Outlook
Address Books by right clicking the folder, selecting Properties, clicking
the Outlook Address Book tab, and checking the "Show this folder as an E-mail
address book" box.  Make sure you restart Outlook after making these changes.