Field Line (Fline) will not display

I have been running through a tutorial about field lines i found on the web;

The script i made all seems to be in order, but the geometry curves for the Field Line node do not show up - I tried baking it to see what would happen and it seemed to bake something, but what ever it was, was invisible.

I am very confused as there are no error dialogues to go by. Attached is the script and rhino file.

Any help is muchly appreciated.


19_At.E_AUD_Site Map Test.01.3dm (204.2 KB)