Soundwise
 
I always had problems when tried to use hacks or optimize OS to my liking. YMMV, though.

I also try to avoid it in general, for the same reason I steer clear of any pirated/cracked software & plugins: it can cause difficult problems that completely destroy your productivity. But Windows Defender has always been a real PITA so I wanted to make sure it is not behind these issues and doesn't run anymore. I can't help but wonder: what where they thinking at Microsoft when they integrated this piece of garbage into the OS.

AnacondaI can't help but wonder: what where they thinking at Microsoft when they integrated this piece of garbage into the OS.

Scanning files isn't always used for a user's security or protection. Sometimes it's a "I wanna know what's in your pockets" kind of thing.

Anaconda
First of all, I think the new Platinum version is very good from the interface and functionality and the subscription model is fair, too. Providing the program via Steam is also a great idea, however...
 
1) Steam download of SONAR does not work most of the time. If I reinstall Windows, I have to try probably 20-30 times during different days to get SONAR to download without the error message "contents still encrypted". I have an active subscription and all of the big games (some even 30-40 GB!) always download without any issues from Steam. SONAR is the only program with this nasty problem.
 
At the moment I can't progress any of my projects at all:
2) Piano Roll View freezes the program almost instantly ("Program is not responding").
3) Cakewalk TTS-1 cannot be used because it immediately freezes SONAR. So I can't open any of my older projects that use it, since the program crashes.
 
I've tried contacting the e-mail support of Cakewalk about these problems, but never get any reply. It's starting to feel as if I wasted a huge amount of money on a non-working program.
 
Some info about my setups:
PC 1:
Windows 7 Ultimate, clean install, genuine copy
No other programs than Steam, SONAR and 64-bit (legit, no cracked/pirated software) VST plugins
Intel i7 (Hashwell) 4770K 3,5Ghz
32 GB RAM
Samsung Evo 850 Pro 1 TB SSD
No anti-virus or other intrusive programs installed
 
PC 2:
Windows 10 Pro, clean install, genuine copy
No other programs than Steam, SONAR and 64-bit (legit, no cracked/pirated software) VST plugins
Intel i7 (Skylake) 6700K 4Ghz
64 GB RAM
Samsung Evo 850 Pro 1 TB SSD
No anti-virus or other intrusive programs installed
 
Audio card is PreSonus FireStudio Project (FireWire). I have the same issues on both PC's. FireWire controllers are Texas Instruments based, which should be reliable AFAIK.
 
Any ideas on how I could get SONAR Platinum usable?

I've stumbled upon something this afternoon which may impact the crashing PRV view.
 
It appears that the Microsoft Visual Studio C++ Redists aren't being installed correctly on certain Windows configurations (usually pending Windows Updates): 

1. Go to [Steamlibrary]\common\cakewalk\_CommonRedist\vcredist\2013\
2. You'll see a vcredist_x86 and vcredist_x64. 
3. Run both of these installers. 
4. You'll probably be prompted to Restart. 
5. Once you do that launch SONAR again and test. 

If you want, you can go through and run the rest of them in the other folders (2008, 2009, etc) if you want to be extra sure.

Re: The "contents still encrypted" issue. This has popped up with a few individuals and it seems to stem from a corruption somewhere in the client install. For some reason the client thinks SONAR is pre-release application (hence the encryption message).

Other users have successfully resolved the issue by:

1. Go to STEAM > Settings > Account
2. Beta Participation > Change
3. • If you are not currently opted into the Client Beta,  opt in.
   • If you are currently opted into the Client Beta, opt out.
4. Click [OK] and let STEAM restart the client.
5. Try the download again.
6. If you were in the Beta, should should be able to opt back in after.

Whatever this does for the STEAM client, it seems to clear the error from happening again. 

Seth Kellogg [Cakewalk]
It appears that the Microsoft Visual Studio C++ Redists aren't being installed correctly on certain Windows configurations (usually pending Windows Updates): 

1. Go to [Steamlibrary]\common\cakewalk\_CommonRedist\vcredist\2013\
2. You'll see a vcredist_x86 and vcredist_x64. 
3. Run both of these installers. 
4. You'll probably be prompted to Restart. 
5. Once you do that launch SONAR again and test. 

If you want, you can go through and run the rest of them in the other folders (2008, 2009, etc) if you want to be extra sure.

Thank you for the answer! I ran  every redistributable EXE from the folder C:\Program Files (x86)\Steam\steamapps\common\Cakewalk\_CommonRedist, including the setups from DirectX and DotNet. I'll report back here as soon as there's something to report - when it either crashes again or has been working for longer.
 
I also have one additional question about PRV: is it possible to disable the note playback when editing? I mean when it plays the notes as you're drawing or moving them. Perhaps this would also reduce the PRV freezing, because often it seems to freeze just when it's about to play the note. Most of the time I have no need to hear the note while editing.
 
And yes, the Steam option "Beta participation" indeed seems to fix the "Contents still encrypted" download issues. I could finally install Sonar on my laptop after reading about that workaround at the Steam forums.