2 part question...if I uninstall Platinum, (Newburyport) will I be able install the latest version without taking out all of the peripheral programs and settings?  And, if the new installation fails, will I be able to reinstall 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it seems like the usual culprits are indeed present on your system, so it may be some other bit of either missing or outdated routine.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
 

Thanks for hanging in here with me Bob.  The problem I had with windows update was that it kept presenting the same updates repeatedly, and every time, the updates would install successfully.  The windows update fix program took care of that issue.  I installed all of the current updates and that problem has not recurred, but I still cannot update beyond Newburyport.  
 
I still want to try uninstalling and reinstalling the latest version of Platinum, but I'm in the middle of a couple projects and afraid of losing a functional version of the program.  What do you think?    

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. 

Qua

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. 

FWIW, when I ran into this error, I actually had to uninstall all of the x64s (all years in the program manager), then run the new installer to get it to work.  Just uninstalling the latest one and installing the new one was not enough for any of my Windows 7 computers.

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?

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?

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.

Keep checking for windows 7 updates. When you have them all, it will install.
 
I was in love with Win 7 and didn't want to go to 10. Now, I love 10 and can't believe I waited so long. So much better than 7, and just as stable. YMMV, of course.

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.