I'm having the exact same problem only with a C400 notebook. I tried to install the WinNT software with disastrous results. I had to re-install Windows XP.
I have since tried the C400 on another C/Port II device and have no problems. The is only two thing I can think of.
One, My original C/Port II device was bad.
Two, the 2nd C/Port II device I used (that worked) was an older Model. Maybe there is something in that?