Shifting Scripts from Mac to Win2000

Hi all.

I'm attempting to collaborate with someone who is using the PTB in
Win2K. My script (HFN.m, available at
http://www.dal.ca/~mcmullen/HFN.m) was programmed on a Mac (ML 5.2, PTB
2.44), and it isn't working on her machine. Instead of seeing the demo
stimulus, she gets a blank screen for the length of time that the
stimulus is supposed to appear.

I don't have a Windows machine here, so I'm left with the unfortunate
task of trying to do remote debugging. The problem is worse because
there are no error messages, the screen simply goes blank for the
correct length of time that the stimulus is supposed to be shown (about
1 minute) and then the script exits normally. I know this isn't much
to go on, but if anyone recognizes this symptom or can offer any
suggestions for things to try, I would very much appreciate it. I
suspect it has something to do with SCREEN('Copywindow'), but that's
just a hunch.

Many thanks,
Charles.