[Newbies] Problem working on "The Laser Game Tutorial"

[Cloz Camong]

After I make the modifications as in Section 3 page 97, I cannot see
the arrows while I move on the grid.
When I come to the page before I have the described behavior, i.e. I
have to click on the white area and the arrow is redrawn.
But in none of the steps on page 97 I can obtain an arrow as
described. I can see one randomly if I make the world menu pop up over
the morph, but that's all.
I have reviewed the code and I'm sure its exactly as in the tutorial.
Can it be something related to my configuration, i.e. last Squeak
version on Windows XP home?
Is there any way to force the redraw?

Thanks in advance for any suggestion.

Regards
Camong