Whenever I log out, Itunes deletes some of its files

I have been having this problem since the last update. whenever I log off or shut down my computer, Itunes deletes some of its own files, because When I log back in i get the message "Itunes cannot not run because several key files are missing, reinstall Itunes." and I then have to uninstall, then reinstall Itunes. once this is done everything works fine. help?

Dell Inspiron e1505 Windows XP

Dell Inspiron e1505 Windows XP

Dell Inspiron e1505 Windows XP