Chapter 2.1 cant locate node

I get this Error:

ERROR: cannot launch node of type [my_cartpole_training/start_training.py]: can’t locate node [start_training.py] inpackage [my_cartpole_training]

What can i do?

i solved it thank you

Just to close this question, the typical error when you receive that error message is when you forgot to provide execution permissions to the start_training.py.
Remember that in order to provide such permissions you need to issue the command:
$ chmod +x start_training.py