Outlook user does not always change

[Matti Ponkamo]

There are three users in my Outlook. After first (morning)
boot of the XP Outlook does not always "re-start" when
changing the user. After a reboot Outlook acts till the
end of the day as it should, I can change from user to
user properly. Two of the users have two accounts and one
has only one account. Though the PC boots very quickly it
is annoying to close possible other programs and start
again. Any advice?