Thanks so much Corey for the suggestion. Indeed the 'Memory Frame Buffer' was ticked when i was rendering attached email. So i have done a few frames of test render right away after your reply. When i UN-tick it, only the render process are running without the VFB. And there are no output written. So i cant see what is vray rendering. I only can see the progress bar..
On the other hand, ive disable VFB and use standard Max Frame Buffer, everything render/output written perfectly without any overlapping image.
So, i guess we cannot use "Render by Layer" using VFB?
