Outlook 2000 Crashing When Scrolling Contacts

Good day all! A client of mine is having a problem with
Outlook 2000. When he is sending a new message and clicks
To... to bring up his list of contacts, the program
consistently quits to desktop when reaching a certain
point in the list. There is no error displayed and it's
not a "crash" per ce, it just quite to desktop as if ALT-
F4 was pressed. When scrolling through the normal
Contacts folder, there doesn't appear to be a problem,
it's only whensending a new message. It also seems to be
when the list reaches a certain consistent point. Does
anyone know what this could be and what can be done to fix
it? Thanks all!