Please go to the 3rd party Focusrite hardware manufacturer’s website for your audio interface and download and install the latest driver available for your specific operating system version.
Afterwards, restart your computer, and open Cubase and go to Devices, Device Setup, VST Audio System, and make sure the driver is selected for your specific audio interface.
If that does not work then I recommend trying different USB ports directly on your computer (do not use a USB hub) and trying a different USB cable.