The rendering didn’t even get started, it crashed before the rendering dialogue box appears.
I didn’t find any files to be corrupt in the vegas projects that wouldn’t render. I tried various things, like making sure all the source files were in the same folder (in case vegas was “losing its way” when it was looking for the files to draw on. I made sure project settings matched settings I wanted to render with (fps, resolution, disable resampling).
It still wouldn’t render.
So I looped a 30 section section and prerendered it.
That worked.
So I rendered the same 30 s section and that also worked.
Then I tried to render a different part of the film, without pre-rendering it and that also worked.
I closed and reopened the project and now I can render all or any part of it, and the render dialogue appears so smartly now as if it the program were making amends.
It may be unscientific but I’d say the render engine is like the motor in a vintage car sometimes, it has to be hand cranked into action.