How to fix Sony Vegas 12.0 blank screen render?
Use VLC to get the actual frame size. You can go to Tools/media information and from there navigate through the tabs to see what the frame size is.

Then enter that information manually into vegas. When you drop your clips in everything should be good to go.

If you are still getting blank frames in the rendered video then I would guess that to be a render setting. You may want to render to a default setting to see if that helps.