You need to install the VCP drivers for your rosstech cable.
I actually tried this, uninstalled VCDS, went to manage devices and uninstalled, deleted the ross-tech driver, removed and reinserted the HEX+CAN cable and selected VCP and used an FTDI driver for the cable. Maybe I did this incorrectly but it didn't work with Galletto. I'll try again tonight but windows didn't seem to want me to do it, warnings every step of the way that it 'might not be right', you know how windows is... 'this isn't certified, are you sure?', 'the world may explode should you proceed, do it anyway?'
If anyone can link to detailed instructions that'd be helpful, otherwise I'll be searching later on tonight when I get home... TIA