So, I just upgraded to El Capitan and I'm having loads of trouble with my KB37 - which I might add was working perfectly under the previous OS. I suspect something has messed with the flash memory in the hardware. Same description of events as you monadayne. I had to go back to my GuitarPort, which is working just fine. Problem is, I need keys and my condenser mic to get my music rolling again. I'm pretty much at a stand still till they decide to work on this problem.
Has anyone figured out a work around? Maybe some way to update the flash memory without Monkey and License Manager freezing up? Mac recognizes the KB37 since the upgrade, but I haven't used it with my DAW yet.