Anybody know why Outlook 2000 would be dropping attachments (specifically DOC's and XLS's -- so I don't think it is a "security" problem).

A co-worker tried sending an attachment yesterday, and the recipient didn't receive it. It looked to the recipient as if the sender forgot to actually attach the files. If we look in the "Sent" box, the message is there, but there is no files are in it. This user was able to send attachments just fine when on Outlook 97.