Jennifer Auguston wrote:

We are using the Microsoft Outlook Personal Folders Backup
tool. On some of the machines we get the error that
thinks the Outlook program is already in use and can't be
backed up. All of the programs are closed.

If the backup tool can't access the PST, then, despite indications to the
contrary, Outlook is still running. Use Task Manager's Processes tab and
look for OUTLOOK.EXE. If you see it, then you know Outlook is still running
and this page may help figure out why:
http://www.howto-outlook.com/Faq/outlookdoesntclose.htm
--
Brian Tillman