Musicman762
I believe someone already mentioned rebooting your PC, but did you do it before you tried executing Sonar in safe mode?

If you open up task manager, you should only see one version of sonarplt.exe running. Sometimes when Sonar hangs, I've noticed that trying to run it again opens multiple processes, none of which will work. I usually kill all running instances and reboot.

The only recommendation I have left is to try that, and reboot your PC. Then execute Sonar in safe mode, as I described earlier (With the shift key). When asked (if you get that far), load the app with no plugins (There should be a dialog that allows you to cancel everything all at once). Aside from that and a hard drive issue, I've got nothing else. Running Sonar in 32 bit mode is not the answer, because without doubt Sonar 63B should run in a 64 B Windows 10 machine...

The reference I made to 32B was in reference to TTS-1, because it is a 32B plugin and it won't run using bitbridge on a 64 B machine, without changing the processor setting. Sorry for the confusion... I was replying to a different issue and posted the 32B thing in the wrong section.

Yep, have tried the sonar-shiftkey-safemode, the app still terminate immediately without any evidence of creating a process. Nothing appears in task manager. There are zero instances of sonarplt.exe. (I uninstalled the 32bit version (which worked apart from the start screen) and reinstalled the x64 version. )

Rather than start Sonar in safe mode, Try and Re personalize by holding down CNTRL + Start Sonar.
You will then see a message about re personalizing Sonar. accept (Yes).
Let it rescan. The Libsef is the Dynamic Library I believe. This should get you in to Sonar.
I also would re name your folders back to originals. When problem solving like this, the last thing you need is another issue to figure out.

When you uninstalled SONAR did you remove the relevant keys in the Registry?
 
https://www.cakewalk.com/Support/Knowledge-Base/2007013392/SONAR-2015-Clean-Install-Instructions
 
 
 
 
 

Bristol_Jonesey
When you uninstalled SONAR did you remove the relevant keys in the Registry?
https://www.cakewalk.com/Support/Knowledge-Base/2007013392/SONAR-2015-Clean-Install-Instructions
 

Thanks this was a good suggestion, but no cigar. I followed all of the steps, but the installed app is still invalid and doesn't run.  My leading theory now is that something else I installed messed up my C++ environment and it's too deep to figure out. I'm going to clean install -- in retrospect that would have taken half the time I have already spent on this. Thanks for your help, and everyone elses!  
 
Posting this message is my last act on this Windows build, see you all on the other side =)

Hello all from a "new" PC =)
 
I gave up on this issue and reinstalled Windows. Everything works again, of course. 
 
For those interested, it took 5.5 hrs from start to finish, including backing up all my data, downloading the Win10 installer, doing the install, adding all apps (Sonar, etc, and FL Studio) and purchased plug ins, and restoring my data, to the point where I could load my current Sonar project without errors. 
 
Thanks to all who jumped in and tried to help. It is a bit of a bummer that I didn't get to the bottom of the issue and didn't learn anything. Thanks for all the help!
 
Chris

After this ordeal, I hope you look into creating an image file of your C drive once everything is working again. I use Acronis on my DAW and I use Macrium Free on another computer and it actually works about as well.
 
If you would have done this you could have simply returned your boot HD to previous state, last saved image. Of course you'd lose any new data stored on your C drive. Yet you could always backup that on a 2nd computer if you have one. DAW are complicated systems and every OS will eventually get corrupted, to the point you give up troubleshooting and just start all over.
 
I’m a little excessive, I save images files every time I make any change to my system, so I can backtrack if needed. System restore is supposed to do this, but it doesn't’ always work. Image files or even a 2nd HD that’s an exact image of your good HD will suffice. I keep my C drive very lean about 50 gigs, the backups are 24 gigs.
 
Hope things are going better for you now.