I just made a discovery about rendering in grid mode. I got a big scene and the bsp tree just dont want to render my scene so i switch to grid just for fun and it work.
My question is is there a differnece of quality betwin both rendering methode?
Keep in mind that mental ray has removed Grid acceleration from version 3. So, try to finish your current job before upgrading to XSI 2. (which uses mr 3)