Vegas 5.0b introduced a bug in reading some of the renderers. If you get this error, you can request an update of Neon which fixes this problem by responding to your original e-mail (send a mail to Gary Kleiner). In the meantime, the following workaround will allow Neon to run:
1) Open Vegas and your project
2) Choose File - Render As
3) In the type dropdown box, pick MPEG1
4) In the type dropdown box, pick MPEG2
5) Press Cancel to exit the Render As screen.