I have a FireWire connected My Passport Studio that show this error since I up dated to El Capitan X.11.3
Yet I use the Drive for Time Machine Back up. And has never used as a Raid device.
I do have also a My Cloud Western Digital NAS Drive. Which I also have some issues with It its attached to Comcast Wifi Modem and have to unplug periodically to reset.
I do open the application asked and lo and Hold it doesn’t even have an adjustment for Raid Drive. I am tempted to just uninstall the WD Drive Utility . I notice the software has had an update in several years. Such software should be updated with every major system change.