[Chuck Thomas]

I got the same error. I managed to solve the problem after some trial-and-error. Here is what I did…(By the way, I am using Vegas Pro 11)

1. I clicked “render as” in the File menu and decided that MPEG-2 was a pretty good default format so I then selected the “MainConcept MPEG-2” preset.
2. After looking at all the “sub” presets (I guess they are just the variants of MPEG-2) I decided I wanted to use “DVD Architect NTSC Widescreen video stream”. This is because I knew I would be using DVD Architect, because I knew I wanted NTSC (a basic TV standard), and because I knew I wanted my video to be in widescreen.
3. Now here is where I think I did the wrong thing…I then decided to “Customize Template” (because I am particular about my videos).
4. The default resolution (with the above preset) was 720 480, but I wanted to use 1280 720 (an HD res which by definition is not NTSC), so I modified that part of the preset to be 1280 720.
5. Immediately after I started the render I got this message: “An error occurred while creating the media file (nameoffile). The reason for the error could not be determined.”
6. When I changed the resolution back to 720 480, the render worked as normal.
7. In order to get a video file in 1280 720 I used a preset that was not NTSC, but rather one that was for rendering HD: MainConcept MPEG-2 HDV 720-30p.
8. I ended up using “MainConcept MPEG-2 DVD Architect NTSC Widescreen video stream” for standard definition video (probably to go on a DVD) and “MainConcept MPEG-2 HDV 720-30p” for HD video.

My theory about why the error happens is that Vegas doesn’t like you to modify presets to a HIGHER resolution than the default resolution in the preset. So basically, if you want to do standard definition video, use the appropriate preset. Likewise for HD.

That is my theory based on my experience with the error. I hope it proves helpful to someone. And BTW, those who posted above helped me get to my conclusion.