Sorry to hear you're still having problems. I should have been clearer, I believe the CP210X USB to Serial Convertor only works one way - it converts from USBXpress to Serial.
Did you get the message:
Successfully converter the device from USB to Virtual Serial. Press any key to exit.
You should be able to reset the mode of the USB data logger (I am guessing that it is currently in USBXpress mode).
First remove the data logger from your Vantage Pro2 and connect it to your PC. Then run the piece of software installed under WeatherLink called CP210X USB to Serial Convertor. Follow ...