I have a new computer with windows 8.1. I have used outlook 2003 on at least 20 different computers, and operating systems from 3.1 to 95 xp to nt to vista to 7 for many many years and never had this problem.
When I start to type a recipient in the To:, CC:, or BCC: box, the computer suggests a username, or a list of usernames (autocomplete), as it should. However, I am unable to select any of the usernames suggested. That applies whether there is only one or multiple suggestions. Hitting a return, tab, or clicking with the mouse leaves the letter I have typed and goes to the next line. Checking with advanced e-mail options shows that the "Suggest names while completing to, ..... (autocomplete) is selected. I have been working on this problem for over 4 hours, getting a little tired of it! - I have never used a 'nk' file in the past, and not sure how to use it in windows 8 if that is the problem (which I doubt).