Hi Tracy,
Have you attempted a "test" project on video and other media?
For a basic "test", I'd suggest you place the Aquarium.mpg into the time-line three times. Do not add anything else. Also untick video thumbnail.
Create disc section
Spanner icon
preferences
Menu
Untick
The video thumbnail...can look cute but it used to cause hassle to some users during the write process.
I also don't know what build you are using.
I also don't know what the make up of your project.
As a general rule for Video Editors it is sensible to have ALL media files in one location (My Works folder is best option) instead of spread all over the place on your PC. I'm assuming everyone knows this... just thought I'd add it.
I had thought I'd localised the cause... but ummmm
Dafydd