the bsp calculator doesnt like polies that are too small. you know the kind that you cant see, sort of what you get when you do a bolean and forget to tie up all the loose ends. also i find that the chamfer tool in ts6 does it at times if you try to camfer something complicated. simply look over anything you did something stupid with, and find those pesky micropolies. by changing the scale you simply make the polie big enough not to crash pcs, none the less its bad practice to use a model with a known and uncorrected flaw like that. i think max's optimise can correct this pretty much instantly.