Need help...Black regeion Area..

[tooviikara]

Hi, Now I am working with Max 2011 supporting V Ray..I have a serious issue, When I try to render a Scene, First time it will render properly, but if I want to render a region in that same render frame window, i get total black area, means there is no rendered image and alpha channel in that rendered region.If I restart max, then the same thing happens again..I get the rendered image only in the first time rendering... Pls..help..