Oh my god. I had the same problem I think.
I fixed it by doing this (okay. the fix sucks, but it works..):
1. File --> Render as...
2. Deselect 'Render loop region only'
3. Render your video. No problems, I hope/guess
Don't know if it works with your guys Vegas, but it did on mine.
obtw, i didnt searched on google. Just was messing around a bit, with the settings, then this was the solution xD