email message converted to attachment

[Sarah]

Recently people have reported that emails they receive
from me arrive with a subject line but a blank message
area and an attachment. It seems the email message is
converted into an attachment for some reason.

I also receive an undeliverable message for these
emails...

Can anyone explain what is happening? My email is set to
HTML and it happens when I try to send a particular word
document as an attachment to the email. I am using
Microsoft Office XP.

thank you for your help!
Sarah