Using Outlook 2007 w/ XP.

I have a distribution list of contacts from my contact file. When I click
on any contact in that distribution list, I get an error message that states
that Outlook "could not find Contact "[contact name and email address]". It
may have been deleted or moved from its original location. Would you like
to remove it from this list."

But the contact is still in my contact file.

Can you tell me what might cause this problem and how I can fix it?

Thanks.

Bob