I had the exact same message just today. The problem was caused by a power blink. All I did to fix it was unplug my interface from the computer and plug it back in. After that I opened cakewalk up and a window popped up that said a new device (focusright scarlett 18i20) was recognized, do you want cakewalk to add it? Just hit yes. This added my interface to the list of outputs I was able to choose from. This can be caused by other things than just a power blink. Its basically cakewalk not recognizing all available outputs.
I had the exact same message just today. The problem was caused by a power blink. All I did to fix it was unplug my interface from the computer and plug it back in. After that I opened cakewalk up and a window popped up that said a new device (focusright scarlett 18i20) was recognized, do you want cakewalk to add it? Just hit yes. This added my interface to the list of outputs I was able to choose from. This can be caused by other things than just a power blink. Its basically cakewalk not recognizing all available outputs.