Digi USB/2 wont install Virtual COM Port

Concering my Digi USB/2 device. On on of my new Win 7 PC:s the driver software will not manage to install the Virtual COM Port needed for proper contact with a controll software. I have tried to re-install but no way. I have also installed the FTDI USB driver separately and it shows up as a Virtual POrt when a another device is connected to the USB port. How can this be?