I just rendered a 5-minute video with Vegas Pro 12. Have done this type of render hundreds of times before. the render template is MainConcept AVC, the file is about 300 MB in size. When I played it back (using VLC, ArcSoft TMT, and Windows Media Player), the video shows distinct bandings of different colors. Please see screenshot. What is causing this? I re-rendered 2 more times, same result.
Thanks!!

perhaps an acidental change in the render template?

Up date any drivers recently? install anything specific that modified something related to video i.e. codecs?

Thanks for your responses. I still don't know what caused it. But I managed to solve the problem, by shutting down the computer, start it up, re-render for the 3rd time. No more bandings. Sometimes I just have to shake my head, guess that's just how computers are.

It can be not only issue of encoder but also bug of decoder of source material codec. In such cases, it is appropriate to disable GPU acceleration for testing.