"To add the clips that you have rendered from Vegas or Movie Studio, in DVD Architect choose Insert > Media, and navigate to the rendered clips on your system."
The rule of thumb is always render your video and audio to compliant forms in separate files as per the previous post. If you rely on DVD Arch to render anything (except the menu) then you will lose quality, waste time and possibly run into problems such as you have.
Yeah.
You don't add your clips to the MENU timeline.
You add them to the MEDIA timeline, per the instruction above.
And they should always be DVDA compliant streams, as rendered in Vegas.