Well, from a quick "glance" at your timeline, you have many tracks with many events at places which either cover up lower tracks OR partially covering up lower tracks. This could be giving you some spurious result on render. Vegas would be doing the correct thing, but YOU might like it! Now I'm not saying you SHOULDN'T do this, but I personally would like to see a more consolidated timeline. At the moment there appears to be no logical laying out of your media?
Could you prepare:
#1 - A blowup/screen grab of your start including ALL your tracks
#2 - A blowup/screen grab of those areas you THINK you are having an issue with
#3 - Could you prepare a simple mov or wmv of the region you KNOW doesn't work and say exactly where this relates this to on your timeline? And ppost these files so we can view them?
Bottom line, you have your media spread out in a fashion, that at present, I can't image just WHAT it would do in a WMV format.
My thoughts aint on the render process - yet! - more on the layout of your project. But I could very well be incorrect!
Getting there .. .