Newbee Jython Question

[Charles Griswold]

I'm just starting to learn jython prior to embedding it in a larger lava 
application.
On my first try I get the following message


C:\Downloaded Files\Jython>java -cp . jython-21 -o jython-2.1 demo lib 
source
try path C:\Downloaded Files\Jython\
can not get flavour null for os 'Windows_XP'

It seems like it doesn't like to run on Windows-XP.
Am I missing some param or flag for Jython to run on XP

I'm sure there is an obvious answer. Any help appreciated