Windows Live Mail Creating Attachments

I live in Japan. I am using English windows XP. My Windows live mail set to at Tools - Options - Send - International Settings: Western European (ISO)

My problem is when i reply an email that written on a Japanese computer Windows Live Mail creating an attachment that one can see at windows pane. I mean you can see the paper clip thing on windows pane. However, once open the email there is no attachment. I think that is happening because of different language encoding. The thing is my Japanese friends think i have a virus in my computer.
Is there anyway, i can stop that attachment thing happening?
I do not have that problem if i reply emails from friends in North America.
I just send to a Japanese friend an email in plain text rather than rich text format. I am not sure if that will make any difference.
Any ideas or suggestions to solve my problem greatly appreciated.
Thanks

 

****Update*** I checked at sent items folder and the email i send in plain text format also has an attachment.