Here's the actual failure 

Unable to Register the DLL/OCX: Regsvr32 failed with exit code 0x3

Sounds like Windows maintenance is not all applied.
 
Bob Bone
 

may need to run the utility mentioned in this post http://forum.cakewalk.com/FindPost/3393935

in my situation i like to re install windows quite a bit.
i like a fresh, clean registry, clean folders, exc.
before i started saving system images, i used to download the windows update packages straight from Microsoft.
this way when i re installed windows, i didn't need to do updates for hours.
been a while since ive done it but it was far more efficient then downloading updates every few months.

To answer two of the questions above, all of my windows updates are current, and yes I tried uninstalling the C++ update and reinstalling it.  Also when I look at installed updates in windows update, I have no failed updates.  Thanks for the suggestions, but it looks like back to the drawing board.

This link has info that might help (it did for someone else who had this error).  Also, in a prior post from Noel for an old thread for the same error, he indicated that the service that is failing is a Windows service they call to register components and that all pending Windows Updates must be completed and then Sonar can be installed.
 
That thread had this link in it as well:
 
https://www.cakewalk.com/Support/Knowledge-Base/2007013353/SONAR-Launch-Error-for-Missing-MF-dll
 
Bob Bone
 
 

 

Thanks Anderton, the knowledge base was the first place I looked for a solution.  Nothing there helped.  And thanks to all of you who suggested making sure that all my windows updates are current, been there...done that.  Also appreciated those who offered the solution of updating, repairing, removal and reinstall of C++.  None of the above has solved my problem.  I've even had 2 sessions with a Cakewalk Support rep. and they can't solve the problem either.  I've been a Cakewalk user since the original version 1 midi sequencer days, and the is the first time I'm actually considering going to another product.  Frustrated..... 

Can you please go to Control Panel > Uninstall a Program, and scroll down the list to see what your latest C++ run-time version is - and post that here?
 
Also - there were a couple times where Windows Update said it was up to date, but in fact there were additional updates to install that were not detected because of a MS bug in its maintenance searching process.
 
They provided the following to help address that:
 
https://support.microsoft.com/en-us/gp/windows-update-issues/en-us
 
Have you looked into the above?
 
Bob Bone
 
 

jazzyd
I've been a Cakewalk user since the original version 1 midi sequencer days, and the is the first time I'm actually considering going to another product.  Frustrated..... 

I seriously don't think going to another DAW is going to solve your issue.  You have a systemic Windows issue that is preventing the installation of Sonar.  Even if you go to another DAW, those systemic Windows issues are still going to be present. 

Best to persist with resolving your Windows issue.  I still believe the issue is with a faulty Windows update installation.  I think robert_e_bone is on the right track with his suggestions.  The issue, I believe, is with a corrupted MS C++ runtime installation.

robert_e_bone
Can you please go to Control Panel > Uninstall a Program, and scroll down the list to see what your latest C++ run-time version is - and post that here?
 
Also - there were a couple times where Windows Update said it was up to date, but in fact there were additional updates to install that were not detected because of a MS bug in its maintenance searching process.
 
They provided the following to help address that:
 
https://support.microsoft.com/en-us/gp/windows-update-issues/en-us
 
Have you looked into the above?
 
Bob Bone
 
 

Bob, the latest version of C++ is Microsoft Visual C++ 2015 redistributable (X64) -14.0.23918. I have uninstalled and reinstalled it, repaired it.
I have clicked on and followed all of the links for Windows update, used the Windows update fix program. The update program tells me that that I have no more updates.  Also in looking at the update files, there are no failed updates.
 
I have disabled my antivirus program and my windows firewall.  
Also, I bought and ran a registry cleanup program, didn't help.  
 
The last working version of Platinum that I can roll back to is Newburyport.    

Boy - this one is a head scratcher. 
 
All indications point to something lacking with Windows Update maintenance, but it seems like the usual culprits are indeed present on your system, so it may be some other bit of either missing or outdated routine.
 
I happen to be running Windows 8.1, so the maintenance won't line up to what you have, otherwise I would have offered to start comparing applied patches to see what was different.
 
I'll poke around some more this morning and see if I can come up with something - I AM convinced it is something with the maintenance.  I had one occasion some time back where it told me there were no more updates to apply, but for some reason I was aware that additional maintenance WAS out there to apply.  I cannot recall how I resolved that, but it was that sort of experience that makes me think there may be something else that COULD be lurking out there to get applied.
 
Hang in there - because this IS a local issue to your system, and not some global issue for everyone, it will just take additional digging and trying, to get down to whatever really is the missing maintenance.  That is actually GOOD news, because it then means this should be solvable. 
 
Bob Bone
 

jazzyd

robert_e_bone
Can you please go to Control Panel > Uninstall a Program, and scroll down the list to see what your latest C++ run-time version is - and post that here?
Also - there were a couple times where Windows Update said it was up to date, but in fact there were additional updates to install that were not detected because of a MS bug in its maintenance searching process.
They provided the following to help address that:

Have you looked into the above?
Bob Bone

Bob, the latest version of C++ is Microsoft Visual C++ 2015 redistributable (X64) -14.0.23918. I have uninstalled and reinstalled it, repaired it.
I have clicked on and followed all of the links for Windows update, used the Windows update fix program. The update program tells me that that I have no more updates.  Also in looking at the update files, there are no failed updates.
I have disabled my antivirus program and my windows firewall.  
Also, I bought and ran a registry cleanup program, didn't help.  
The last working version of Platinum that I can roll back to is Newburyport.    

Okay, I've been go round and round on this too. I'm on Windows 8.1 and have had the exact same experiences as jazzyd has been going through on Windows 7. Mine too ran great up to and through Newburyport. After reading through all this and repeating everything with no fix, I decided to just uninstall C++ is Microsoft Visual C++ 2015 redistributable (X64) -14.0.23918 completely without re-installing it.  Running my install from a downloaded file, this time Sonar seems to install great and when I went to check the Programs/Features the MVisual 14.0.23918 had indeed installed itself.

Maybe this is an 'order of operations' problem? IDK, but try uninstalling the last Microsoft Visual and running the Sonar installation without it. I'm finally up and running by doing it that way. 

The 0x3 error code indicates a file or path not found. Did you happen to have any indication of what dll it was trying to register?

Man, you've been through the wringer.  Given the time involved, I would definitely do a clean Windows 7 install, ask chuckebaby for the link to "download the windows update packages straight from Microsoft" he mentioned (rather than using Windows Update), and then reinstall SONAR and all your other programs.  It's a pain but it'll probably save you time tracking down those pesky  errant bits.

jazzyd
Here's the latest.
 
In the Cakewalk Command Center, I right clicked on the Platinum top line and found 2 uninstall files. I uninstalled them one at a time and ran the Platinum Update in between the uninstalls and the updates FAILED.  Then I uninstalled both at the same time and ran the Platinum update and it FAILED.  Fortunately, after each failed attempt, I was able to roll back to Newburyport. 
 
 
I uninstalled the last version of C++, then ran the Platinum update and it FAILED.  Then I uninstalled all of the (X64) versions of C++ and ran the Platinum update and it FAILED again.  I hadn't checked Windows update to see if there updates available, so I checked and found 3 updates.  I ran the updates successfully and then rebooted my system.  I ran the Platinum update again and it FAILED.
 
The .dll's that are not registering are the following: (Note: not a complete list)
C:\Program Files\Cakewalk\Shared Utilities\CW120Auto.dll
C:\Program Files\Cakewalk\Shared Midi Plugins\Arpeggio.dll
C:\Program Files\Cakewalk\Shared Midi Plugins\ChordAnalyzer.dll
C:\Program Files\Cakewalk\Shared Midi Plugins\EchoDelay.dll
C:\Program Files\Cakewalk\Shared Midi Plugins\EventFilter.dll 
 
Thanks, any new ideas?

Uninstall all of the x64 versions of the C++, then Install the newest version before running the Platinum update.
 
https://www.microsoft.com/en-us/download/details.aspx?id=48145
 
I had the same error you posted in your second post, this is how I solved it.