What are your machine's specs? Have you updated the Fireface's firmware to the latest version?
This is taken from the RME forum (http://www.rme-audio.de/forum/viewtopic.php?id=7348
Installation of RME Audio Interfaces under Windows 7
The procedure and instructions found in the manual and here are all fully correct and stay valid, except for the start of the installation. In Windows 7 Microsoft removed the automatic start of the Driver Software Update dialog - thank you Microsoft!
Therefore this dialog has to be started manually after the failed driver installation.
- Hit the Win key, type 'Device Manager', start the Device Manager by selecting it from the list and hit Return.
- The device is shown with a yellow warning symbol. Usually it is already found in the correct category, Sound, Video and Game Controller (Plug & Play detects a multimedia device). The Fireface UC is even shown with its correct name.
- Right click on the device and select 'Update Driver Software' from the context menu.
- The dialog 'Update Driver Software' appears. Now follow the instructions given in the manual.
And here's the link for the latest drivers:
Make sure to uninstall all drivers/RME software in your machine and then reboot prior to reinstalling to make sure everything is erased.