[flexcoders] file.upload() works fine on mac os x, does not work on a PC

[tchredeemed]

I tried this in all browsers on my mac (firefox, safari, camino), and it 
uploaded fine.

I tried this on all browsers on my pc (firefox, ie6, ie7), and it did not.

file.upload( new URLRequest( 
_appGlobals.serverURL+"data/attachment/?order_id="+_appGlobals.order.id ) );

serverURL = https://www.oursite.com/

order_id is set

for some reason, it is faulting!  any ideas why?