This error for Sony Vegas happens at rendering. It happened for me at 25% when I was rendering my first video.
How I’ve managed to fix it?
This was very simple. Build your video by adding the video and audio content, even add effects then save the project. Close Sony Vegas.
Open the project and try to render the video. The error should not appear anymore.
I am using Sony Vegas 10 but this trick should work also for older versions.