Now that's strange. As I said, it ran perfectly on my system with 6.31.4, even after having bought my new graphics card (gf4 ti4200, 64MB -> gf6800 gt, 256 MB). I'm still confused due to the fact that the cubemap is not as big as 4096x4096 which is not only the texture size limit for my new card, but also for the older gf4, if that is of any help to you. Weird thing...