I had the same problem. Strangely, it worked in XP virtualization mode, but not natively in Windows 7. It turned out to be my Logitech keyboard. Once I figured out which of the many HID's (installed by Logitech) caused the conflict, my problem was resolved.

What I do now: each time I want to download a new or updated config, I go into the device manager, disable the culprit HID, start PEP, plug in my TSU9600 and download the config. I then re-enable the HID.

Not the perfect solution, but it works.