thanks guys. but there is nothing wrong with the model. i checked it thoroughly.
as for trying to do a methodical troubleshoot, my max crashes every time i try to render it with an override material. not sure how to get around it. i tried it with another light source, vray sun from another angle. but that bright spot is not fixed in that.
but when i rendered that region alone with the vray dome light that spot is fixed but the region borders are visible.
@macker, that setting has worked well for me till now, as it always takes a lot more time when i use higher settings. and this is the first time i am came across this issue. maybe it might be fixed in higher qualities but that does not explain how it got fixed when i rendered the region alone.
i am really confused as to what the problem might be.