Tutorial 10 - getting Traceback

[RichardMorris]

Hi, I'm at the second section of the Python tutorial, setting up a program to adjust street widths. I've loaded Tutorial_10_Python_Scripting/scenes/02_PythonScripting.cej scene and followed the program input instructions but am getting this traceback when I run the program for the first time:

Any suggestions welcome

Thanks

Richard