Outlook outgoing mail duplicate

I have Outlook 2000 running on Windows XP Professional. When sending an attachment from Windows Explorer, a copy is sent to the recipient but another copy sits in my Outbox’s “unsent”. The Outbox copy will be missing the text I typed in the email.

On another occasion, when performing the same task the mail was sent but the text I had typed was missing form the document the recipient received – although the attachment was still there.

Any suggestions?
Our virus software is ESET NOD32 3.0.621.0