I’ve tried all the suggestions above, but nothing works.  I still get absolutely no sound output from Sonar X1.  Uninstalling and reinstalling Scarlett mix control had no effect.  Changing name of aud.ini file had no effect.
What can I try next, as I am totally “dead in the water”, if you know what I mean?
 
Thanks.    - Greg

When you renamed AUD.INI did you get a new one generated when Sonar started?
No other apps open?
Sure you have mix control configured correctly?
Use a brand new project.
 
Again are you running X1D?

Sounds frustrating.  For troubleshooting, I'd stop the computer sound in control panel and also try mme/wdm drivers in your focusrite software if it's an option.
 
Well one thing... system restore.  You could try that.
 
Basically though, I don't have a clue.

Well I'm happy to report that X1 and Scarlett seem to be working together normally now, even though I made no changes since my last post.  It's strange why one minute it's not working, then the next minute it is, with no changes in between.  Should I start believing in ghosts??  FYI:

• After a renamed aud.ini, and restarted, a new aud.ini was generated
• I have the Scarlett mix control configured exactly the way it has been working fine for over a year
• I have been running Sonar X1D

Hopefully things will stay normal and I thank you all for your help!!! 
 
Greg
Big Fan of the Cakewalk Forum!

That's probably all it took. When you rename or delete the Aud.ini file, Sonar generates a new one based on your default settings.

The reboot probably cleared settings from memory and allowed things to load as they should

Excellent news.

Thanks mudgel!  FYI:  I was pretty sure I rebooted after renaming aud.ini, then found it not working at first, but then again, my Islay single malt scotch may have been playing tricks with my mind.