Hi.
Did you double-check that you have rendered both (video and audio) files to the same folder with the same name. Also check Project properties (video and audio format) in DVDA Studio.
I use a folder like C:UsersxxxxDocumentsVegas Movie Studio HD Platinum 11.0 Projects and separately rendered video (DVD Architect video stream) and audio files like ProjectX.mpg and ProjectX.ac3.