I'm working on this Space Bookmobile Motion Scene (new project) and have already imported a "only for practice" person (consisting only of torso, hips, thighs, shins, and feet segments which I cut out in Phohoshop) and have already parented these body segments.

This time I'm following Lesson 4 - Animating a Scene from my copy of the Official Adobe After Effects v7 Classroom in a Book, in which case I'm using my own files instead of the files from the book's CD (using my own files helps me learn this stuff better).

Ok, this practice person is in the desired starting position in this outer space bookmobile, and he has to walk using legs from the starting position towards the camera (see Original photo);

This person is wearing blue jeans, has white "shirt tails" hanging from underneath the yellowish/orangish plaid shirt over his hips. The CTI (current time indicator) is at the start position in the timeline.

As I try moving the CTI to the right in order to begin following the lesson from the book to the right at 15 seconds/frames (or whatever - please bear with me, I'm a first timer in Adobe After Effects) the whole background scene suddenly changes to these goofy colors (actually, this happens when I move the CTI to the 01 second/frame mark), but the practice person stays the way it is in the original scene (see photo);

Then, when I try moving the CTI all the way to the right (the end of the time line), this goofy color change remains but just as in the above scene, the person stays the same way it was in the original scene (with the CTI at 0 seconds/frames) (see photo);

Why is this happening and how do I fix it?  My computer specs are Core 2 Duo @ 2 GHz,

                                                                                 lots of HDD space (~over 50 % if I'm not mistaken),     256 MB Nvidia GeForce GT 8600M video card, MS Windows XP Home_sp3, I have not messed with any of the default settings on this computer, but left them alone, this computer is a Dell XPS M1530 laptop, and I believe it's specs are more than adequate for running AAF v7 with with ease.

Thanks in advance.