It looks to me that it isn't a 'Light' problem. I've rendered a scene (with vue 4.06) under Windows ME, with over 120 lights, all casting shadows, and approximatively 20 of them having volumetric settings. It took a REAL long time to render, but I did it ! :-) Maybe a glowing materials problem, because I'm actually working (with Vue 4.1, this time) on one scene that sometime freeze... A thing that worked for me one time was to select all elements of your scene, except camera, and save it as a .VOB file. The creating a brand new file and re-import this object... You could try this... Hope it could help...