Hi,
I had exactly the same problem (Windows XP German). However, I just tried to reinstall the software and the USB driver. After some attempts, it surprisingly worked. I’m not sure what the problem actually was, but now I can upload firmwares. I still got some problems with the firmwares (some don’t work), but I don’t know if this has anything to do with this strange USB driver problem. I hope you’ll make it!
Greetings