In response to your question, I have attched the .blend file. Actually, the animation I'm trying out is trying to explode a virtual car in a line of real cars. The simply vanishes from the screen at the frame where it is supposed to explode. When I first did the car explosion, I set the explosion at between frame 50 and 51 without the camera tracking and it went on well. So after setting up the motion tracking from Voodoo in Blender, I then appended the car and changed the frame to 1000 and 1001. Then the problem starts. I feel disappointed because this was supposed to be my first major project  where I did everything myself, from the modelling of the car to the eventaul exploded car in the real life footage. But somehow, I managed to mess things upHope the .blend file helps . Thanx for replying