That solution is to use WASAPI shared mode :)

Hey Noel - just to follow up, here's some more data for you. If I open any SONAR project with WASAPI Shared and the MIDI Playback and Recording driver mode set to MME, the MIDI keyboard isn't recognized. If I change the MIDI driver mode to UWP, everything works fine. Maybe it's system-specific?
 
I haven't tried this with WASAPI Exclusive or with CbB yet. (I'll be installing CbB soon on my main music computer, I just wanted to make sure I had all the Platinum stuff on the computer before doing so. I'll test this on my studio B computer that has CbB installed to see if it happens.)

"Solved" in the sense that is must be system-specific, because on a more recent computer, both MME and UWP work with WASAPI shared using either Sonar or CbB. However the issue remains repeatable on the older machine. I blame Windows 

Anderton
Hey Noel - just to follow up, here's some more data for you. If I open any SONAR project with WASAPI Shared and the MIDI Playback and Recording driver mode set to MME, the MIDI keyboard isn't recognized. If I change the MIDI driver mode to UWP, everything works fine. Maybe it's system-specific?
 
I haven't tried this with WASAPI Exclusive or with CbB yet. (I'll be installing CbB soon on my main music computer, I just wanted to make sure I had all the Platinum stuff on the computer before doing so. I'll test this on my studio B computer that has CbB installed to see if it happens.)

if I understand you are plugging in a USB MIDI keyboard in MME mode and somehow WASAPI shared mode affects the MIDI device showing up? Thats really strange since WASAPI deals with audio and not MIDI. 
I'll try and follow up with Microsoft in case they have any clues. 

Thanks Noel. Sorry to bother you about this. MIDI does work with UWP when WASAPI shared is selected. But again, unless someone else can reproduce this, I'll have to assume it's system-specific so probably not worth spending your time on it...you have bigger fish to fry right now 

Not sure this is related, but I have an Alesis Q49 that I have been using for a few years now. Just recently Windows wouldn't recognize it, so I couldn't use it in any DAW I have. Google searches didn't turn up much of anything either. So I put it down to Windows updates as that was the only thing that has really changed on my music machine.
 
After reading something someone had wrote about another problem with a USB device and Windows updates, it was suggested to try another USB port. I did that and now I have the Q49 back working. Using ASIO (RME 400 Fireface) and UPW.
 
HTH 

Grem
Not sure this is related, but I have an Alesis Q49 that I have been using for a few years now. Just recently Windows wouldn't recognize it, so I couldn't use it in any DAW I have. Google searches didn't turn up much of anything either. So I put it down to Windows updates as that was the only thing that has really changed on my music machine.
 
After reading something someone had wrote about another problem with a USB device and Windows updates, it was suggested to try another USB port. I did that and now I have the Q49 back working. Using ASIO (RME 400 Fireface) and UPW.
 
HTH 

I remember a discussion on the forum a year or so ago about resetting USB ports. Windows allows a limited number of devices to be plugged in to any given port. I don't know what the number is, but if, for example, it's 10, the 11th USB device you plug in to that port won't be recognized. I found this info here. Maybe it will help:
Scan For Hardware Changes Using Device Manager

1. Right click Start then left click Run
2. Type devmgmt.msc and click OK, which will open Device Manager
3. Right click on the name of your computer, and then left click on scan for hardware changes.
4. Wait for the scan to complete and then check your USB device to see if it works.

Disable and Re-enable the USB Controller

1. Right click Start then left click Run
2. Type devmgmt.msc and click OK, which will open Device Manager
3. Locate Universal Serial Bus Controllers in the list
4. Click the arrow next to the little USB cable so that it points down instead of to the right
5. Right-click on the first USB controller in the list and select ​uninstall.
6. Repeat step 5 for each USB controller you find.
7. Turn your computer off and then back on again.
8. Windows will automatically reinstall the USB controllers, so check to see if your device works.

I found those same instructions Larry when I was trouble shooting my Q49 problem!! 
 
Great minds think alike!!