i got it. your erreor does not depend on the skybox, it occurs even if it´s deleted. so there are several possibilities:

a) you didn´t include the cls file properly
b) you have another block in your level with a sky texture that i´m unable to find
c) your car action is strange (the tutorial car code looks different)

[edit] AAAAAAAAAAAAAAAAHHH! i don´t believe it!
look at the level strings u typed in your v0_1 wdl ^^
man, load YOUR level, not the Vehicle_playgrond and all works fine ^^

LOL

and, btw, check your camera script, it produces funny errors... eg, it sets your car to the camera position after a few seconds and gets stuck^^