[Blink Berg]

It occured (in my case) that the video which I put in Sony Vegas was compressed with XviD MPEG-4 codec previously and it occured that it should be an uncompressed file. When I made it uncompressed with Virtual dub program everything turned to be fine. Just save your video as an uncompressed file, then put it into Sony Vegas, do what you want and render it in the video format you wish.