Genny,
I think I figured out the problem. ITs the mia materials the author used. I have replaced it with maya and the render is fine.
However, I know you helped in the scripting issue. While the problem was solved, I noticed another serious problem and that is when i move the tank, it treads rotate accordingly on the path. Later down the road, some tread lose their upVector position and flip. I can live with this as long as I am not doing a long movement however, I would like to find a solution to it. I will send you the file as I did before if you like to look at it. thanks again for always helping.