MS Outlook 2002 Problem

I have upgraded our administrative offices from Office 2000 to XP. Since that upgrade, their Outlook does not work properly. For example, every shortcut or item that they click into displays the following message:

?Unable to display the folder. Microsoft Outlook could not access the specified folder location. The folder no longer exists.?

What happened to the folder? Why wouldn?t the Outlook 2000 just upgrade to XP as did Word, Excel etc.? What do I need to do to get these features to work? They would especially like to be able to see what they have sent.

OS: Both Windows 2000 and XP

A huge ?thank you? in advance!