attachments not getting through

I'm using Outlook. With several people to whom I e-mail attachments, all they get is a 'win.dat' statement and no attachment. This started happening in the past 6 weeks. One of the recipients is a Cox subscriber. Others are aol.com or snet.net If I send through Cox.webmail, the attachments go through. All of these people got attachments previously.

Anyone have any thoughts?

Thanks