Outlook 2003 sending multipe copies of email

I have a problem that maybe others have as well wherein upon sending email with an attachment, it will continue to send the same message to whomever directed at about every 3 minutes. Trying to stop it in the Outbox is not possible unless I go into the Task Manager and select End Process. My system is XP Professional, and Outlook 2003 with a duo core 2 Intel Chip, and 2 gigs Ram and plenty of hard drive space. Is there some configuration that I have missed or what?

Thanks in advance to any and all responses.