VIDEO MISSING in .avi file

I created an audio/visual file using Camtasia. The file extension is .avi
file and when I click on it plays perfectly. I copied it to disk, and when a
coworker brings the file up in Windows Media player on her PC she only gets
the audio. The same file on the same CD, or playing from my hard drive,
works fine on my PC. We both have Microsoft Vista operating systems and 2003
Office Edition software.

Any ideas why she can't see the visual part of the file?