Vista - windows mail locks up receivers email programs

I have sent out emails to a "group" and one particular person in this group says whenever she gets an email from me (and ONLY from me) it locks up her whole email program. I have Vista, use Windows Mail. In this email I used stationary from the Windows Mail program, inserted 2 pictures, and added a midi as background sound. No one else reports having this problem with my email. She also has Vista and uses Outlook as her email program. Any ideas why my emails only would do this.

Could be the stationery, and more likely the midi than the images
Have you tried taking this out?

To be honest, if every time I opened an email from a particular person my system started playing a sound, I wouldn't be opening their emails any more ...