Outlook – No file attachment

I have one Outlook 2000 user (Exchange Server 5.5) that whenever he sends a message the “paper clip” indicating an attachment appears even though he never actually attaches any files. It starting happening recently (after setting-up an auto-reply when he was on vacation). Any ideas why all the emails from this user say there is an attachment when in fact there isn’t? The client is using the “Internet Only” Outlook client (a remote users without an Exchange Server on-site).