Unable to reopen contacts in Outlook 2003

I have a user that when he opens Outlook and goes into his Contacts list, it appears fine. If he goes into his Inbox and then tries to go back to his Contacts, the button will appear active in the navigation pane, but his Contacts will not open this time, his Inbox stays open. If he restarts Outlook then he can get back into his COntacts, but the same problem occurs if he tries to go back to them at a later time. Is there any way to fix this without reinstalling Office?