I have video stream and ac3 audio stream rendered in vegas for surround sound. Version 1.0 works fine because it has an option to input both video and audio. In 2.0 When you can't select both only 1. But when I select the mpg it doesn't find the audio for it. It does find the audio if I insert it into the menu but not for the introduction.
You can still add the audio either by dragging the audio file from the explorer window to the audio track in the timeline window or by clicking on the change filename button in the properties window under Media Properties | Track Media | Audio 1.
I've been getting this kind of thing periodically as well, not just with the Intro media. I have been dragging the audio onto the timeline, and aside from temporarily messing up the disc size estimates, it does work out fine in the end. But something seems a little wacky there.