I separated meshes into groups by name to see if I could break down what objects are causing the problem. I got everything, Cones, Nightglow, Walls, obj, objc, (and the rest) to import. It is really hard to say what went wrong. It looks like something went fubar with materials. obj_429.gmt has material roada1508 assigned to it although there are no textures assigned to any of the shader levels. A lot of the other "tree-looking polygons" are not showing any textures. There is a car mesh (obj_49) with no texture. If I had to guess I'd say the png textures are doing it. I would use tga if you can't be bothered to convert to dds. Hopefully you have an earlier version that opens in BTB. Since I am falling asleep I'll see if I can get you a list of textureless objects later this week. At 397 material names, and thousands of objects and millions of polygons the entire track is taking huge amounts of memory to open, so much so that it is crashing max. :S
Once you get back to editing double check your xsectors, one of them doesn't intersect the ground plane and could be missed, I didn't check the other 2.
later