Moving e-mails in Outlook 2002

When trying to move large amounts of e-mail from one
folder to another, I get an error that says: Can't move
the items. Some items cannot be moved. They were either
already moved or deleted, or access was denied. We are
running Exchange 5.5 on NT server.The client computers are
running Windows 2000. One person can only move one e-mail
at a time, and it would take hours for him to move them
all. Are there any known work arounds or fixes?