Since upgrading to SONAR Platinum my older Oxygen 8 MIDI controller does not work.  I have settings the same as X3, where it still does work.  Wondering if the controller itself would not be supported?  It's going through my Focusrite 18i8.  Again - works perfectly fine in X3, and compared settings in preferences.  Any ideas?  Was going to reach out to support, but thought I'd start here.  Being a MIDI newb, wondered if since my controller is really old, maybe I need to get a new one, or maybe I'm just doing something wrong?

Go to "Edit > Preferences > MIDI - Devices" and make sure the Oxygen controller is selected (or if you are connected using a MIDI din cable to the interface that the MIDI ports on the interface are selected).
 
After that make sure you have the Input Echo button engaged on the MIDI tracks and that all your track routing is correct.
 
Check those things out and come back if you still ahve problems. The device should be perfectly useable.

I assume you're using the 5-pin DIN connector in the 18i8. MIDI data is MIDI data, it shouldn't matter how old the device is that generates it. If the preferences and settings are correct in sONAR and you still get no joy, it might be something else together, like a bad cable, something misset with the Oxygen itself, or the Oxygen might have chosen a coincidental time to die.
 
Try using the Oxygen MIDI out and the same cable with a synth or other MIDI device and see if it responds.  

Wouldn't be a bad cable if it is still working in X3. Gotta be settings. Check your MIDI track Input. Set it to the Focusrite Omni entry... and as I said be sure you have the Echo button enabled on the track and that you have the MIDI inputs for the Focusrite enabled in your MIDI Preferences.
 
Also, make sure you actually have a preset loaded in your synth and that the synth is properly routed to the track.

Well I feel really dumb.  I restarted, and it works now!  I had set it up, tried it, no Bueno.  But after a reboot, things are good to go.
 
Thanks all for your suggestions!

I forgot to mention... turn on/connect the device BEFORE opening Sonar. Sometimes things can get weird if you turn controllers on after Sonar is open.  Also wait ten seconds or so before opening Sonar after turning on the controller. That gives the system a chance to detect it. I do not know why this affects certain devices but not others.
 
Glad you got it working.
 
Edit: I'm not sure if this is the case when connecting VIA an interface using DIN cables. I've only used USB input so far.