Why do Microsoft Office Outlook 2003 and Outlook 2002 show different free/busy information for the same users? In Outlook 2003, many users show the hash marks and the no free/busy information could be retrieved message. In Outlook 2002, I don't see the hash marks or the message for those users.
Most likely, Outlook 2003 shows the no free/busy information could be retrieved message because the user never created an appointment. Why Outlook 2002 doesn't show a problem (only no appointments), whereas Outlook 2003 notifies you of one, is a separate question and one I can't explain.
For a straightforward walkthrough of how free/busy publishing works in Outlook 2003 and Microsoft Outlook Web Access (OWA), check out the Microsoft Exchange Team Blog post "Free Busy generation process" at http://msexchangeteam.com/archive/2006/08/04/428597.aspx. Note that for Microsoft Office Outlook 2007 clients running against mailboxes on Exchange Server 2007, free/busy information will come from a Web service—pulled in real time from the mailboxes—not from a free/busy public folder. For more information about free/busy information, see "The Free/Busy Map," September 2004, InstantDoc ID 43152.