Rendering AC-3 Audio for DVD Architect

I am desperately trying to finish my first "proper" project by tommorow night but I've been ambushed by a gremlin. I've tried several times to render the audio in AC-3 format for prepping to DVDA. The associated rendered MPEG2 video file size is 3.68GB so it's a fairly large project. It took just under 9 hrs. I first did this project in 2006 in Vegas 6 to send to my son overseas but this time around I have added a music soundtrack using Vegas 8. The project has 4 video tracks and 4 related audio tracks with an extra track for the music (9 tracks in all).

The rendering process gets to 2% on the meter then goes no further but the time counters keep running. The default selection was "AC-3 Studio AGC On" and the Custom button was greyed out. On one occasion I let the remaining time counter run out to more than 12 hours. Project name is Europe2006001.veg, video name is Europe2006_070508 which is what I was also using to save the rendered audio. I even tried saving the project as Europe2006_070508.veg without success. That's where my knowledge ends (before it begins really). I also created small projects for an intro and the credits and both those audio files rendered OK. Is this a common problem? Should I try another format? Thanks for any input.