Woohoo, physics problem. I'm using default warthog physics and I get this error when I try to add the vehicle to the palette:
11.27.09 09:58:20 EAX: 0x00000000
11.27.09 09:58:20 EBX: 0x0013C201
11.27.09 09:58:20 ECX: 0xFFFFFFFF
11.27.09 09:58:20 EDX: 0x039A30C8
11.27.09 09:58:20 EDI: 0x0013BD08
11.27.09 09:58:20 ESI: 0x00000000
11.27.09 09:58:20 EBP: 0x0013BBE0
11.27.09 09:58:20 ESP: 0x0013BBD0
11.27.09 09:58:20 EIP: 0x7C90E514, C3 8D A4 24 ?????
11.27.09 09:58:20 EXCEPTION halt in \halopc\haloce\source\physics\physics.c,#1005: &linear_acceleration: assert_valid_real_vector2d(1.#QNAN0, 1.#QNAN0, 1.#QNAN0)

I had a vehicle that used warthog physics before, and all I did was update the model and collision geometry and now the physics don't work. But only on this vehicle, the regular warthog is fine.