Problems with the exercises from the Panda Beginner's Guide

Hello I bought the Beginner’s Guide 1.6 Panda3D book and since this time I’m studying and doing the exercises everything was going well until I get to chapter 5, specifically in the Have a go Hero - Adding AI to the Cycle. I Did all the steps when viewing the sample files, but when I try to run my program outputs this message:

Traceback (most recent call last):
   File "", line 24, in <module>
     w = World ()
   File "", line 15, in __init__
     self.track = Track ()
   File ".. \ Panda Projects \ BGP3D \ BGP3D \ Chapter05 \", line 8, in __init__
     self.trackLanes TrackLanes = ()
   File ".. \ Panda Projects \ BGP3D \ BGP3D \ Chapter05 \", line 24, in __init__
     markers = self.createMarkers (MarkerEgg)
   File ".. \ Panda Projects \ BGP3D \ BGP3D \ Chapter05 \", line 49, in createMarkers
     vertexPool.getVertex vertex = (count)
AttributeError: 'NoneType' object has no attribute 'getVertex'

I think this can be any mistakes in class because when I try to run the sample files that were written by the author of the book the same error persists, I do not know how to solve this. Can the author of the book give me a help on this? Thanks.

It looks like vertexPool is not instantiated properly. I don’t know how I can really give more help without seeing the code.

I know this thread is over 2 years old, but if anyone is still using this book like I am, they are going to want to know the answer to this question. This error occurs if you don’t follow the books suggestions on where to create your files. If you create them outside the BGP3D folder make sure to check this line:"…/Models/Markers.egg") in
And adjust it so that it points to the BGP3D folder.
For instance:“BGP3D/Models/Markers.egg”)
for just outside the folder.
I hope this helps other who run up to this point and discover this problem.