I was having the same issue and tried everything I read on the web.
I was able to reslove it by changing the Vegas temp folder to one of my other hard drives. A different physical drive other than my “C” drive.
I also set the program priority in Device Manager for Vegas to High. I was finally able to render my video.
Not sure which one did the trick, but it works now. 2 hour HD video with well over 100 GB of source video, music, etc. DONE!!