Focusrite drivers

There are many Focusrite users, but you will have to provide at least some information about your setup for them to help. Which interface, ASIO or Java EXCL or plain Java drivers in REW, for example. It would probably be worth including a screenshot of your REW soundcard preferences.

Just FYI, I'm currently making some extensive loopback measurements with the Focusrite Scarlett Gen 4 (to characterize it) for distortion testing and have made one Scarlett-to-V3 Mono measurement. So far the Focusrite drivers have not been an issue. ASIO drivers in Windows 10 Pro in a laptop @48kHz. I've also run it in an old Dell desktop with no issues that I can recall other than when the output over-drove the input.

As an aside, I have had a curious issue with the (very old) M-Audio Delta 410, but that card is a 1998 design. Still remarkably good considering. That issue may be the driver that was never targeted for Windows 10, but with proper REW settings I ultimately got it to work. But to reiterate, I've never had a problem with the Focusrite drivers, they seem rock solid with REW.

That error message comes from the Focusrite driver, not from REW.

Happy to hear it, but nonetheless that message is not caused by or generated rom REW.

Note that if you have installed a 32-bit version of REW a 32-bit ASIO driver will be loaded, which may be different from a 64-bit ASIO driver.