Both X2 and X3 have to be installed as "Administrator" by right clicking on the Setup file
and selecting "Run as Administrator" just as Mudgel said.  This will allow the programs access to what
they need to be installed.  There were many errors when extracting files and running
installs without doing this.  I'd try this first, and if this fails, then contact support.

I'm running X3b on Win 8.1 without issue, but that's not to say that something in 
your system isn't preventing it from installing.  Make sure Virus Protection is off also,
as this can also play havoc with the installation process.

I have been installing or trying to install as Administrator, as mentioned in other posts on this thread. The 32 bit version installs and works without problems.   Being a computer tech, I have went beyond in trying to install or fix the original problem and it won't work. 
 
I have two different PC's with Sonar 64 installed, one with X3b and another with X2 and they both have the same identical problems. They were working with Windows 8 and after the 8.1 upgrade Sonar now will not start with the "MSVC100.DLL error.  That was what started the attempt to reinstall as the notice from Windows was to reinstall the program to fix the problem.  The MSVC100.DLL file is in the two required locations and it is not a problem with the file, the problem is Sonar not being able to find/access the file.  I am not alone with this problem, it was reported by another person to Sonar support over a week ago.  I reported it to Sonar support on Monday, but they have not responded to either report.  I've seen other reports of this problem doing a google search, every one of them, that I looked at, says to reinstall the program.
 
I also work the Windows 8 forum and there are a couple reports of audio not working after Windows 8.1 upgrade and users not being able to reinstall the audio drivers.  I'm not sure what else. 
 
Roland had to issue updated drivers for Windows 8.1 for their products to work. 
 
As has been mentioned by someone else and what I found on another web site, X3c program update is supposed to address Windows 8.1 compatibility.  I'm going to have to wait for that and see what happens.

I wonder if it's the version of MSVC100.DLL coming into play...
 
Googling turns up quite a few scenarios where this c++ redistributable is the focus.
 

I've addressed the MSVC100.DLL versions and that is not the problem.  The versions I have in Win 8.1 are identical to the versions I had in Windows 8 when Sonar X2 and X3 worked (and are identical to the versions I have in Windows 7 that X3b 64 bit works OK in)  Actually, I've been through every scenario that I can think of (many not mentioned here) and nothing makes a difference. The error message about that DLL is to "reinstall Sonar".   I can go back to Windows 8 with a Macrium drive backup and it will work, but that is not the answer, as that was something I tried - rebuild the drive from a pre-8.1 backup and Sonar X3b working then reinstall the 8.1 upgrade. 
 
My only answer (and possibly for others with the same problem) for a fix for the 64 bit version is to wait for the overdue "c" update which is supposed to address 8.1 and see if that fixes it.
 
I originally started this thread in case others had the same problem (and there are others from posts).
 
 
 
 
 

Gotcha....

I installed X3b before I did the upgrade to Win 8.1, so maybe that is why I didn't see the problem.

Maybe roll back to Win 8, install the 3b patch, and then do the 8.1 upgrade.

Just a thought...

EDIT: Saw you tried this...

Well X3c was a bust.  It has the exact same problems as X3a and b.  I'm still getting the same error when I try to run X3 64 bit in Windows 8.1.  X3c installed ok on my Windows 7 installation (but I wasn't having any problem in Windows 7).

fireberd
Well X3c was a bust.  It has the exact same problems as X3a and b.  I'm still getting the same error when I try to run X3 64 bit in Windows 8.1.  X3c installed ok on my Windows 7 installation (but I wasn't having any problem in Windows 7).

Sorry you are having an issue. May I suggest a quick call to our support line. Perhaps, they can try to iron this out for you? Hope we can get this resolved soon.

I submitted an e-mail support request Monday morning.  I've heard nothing yet.  That was after I opened CWBRN-10980 that was immediately closed and directed me to contact support.  Another user, that has posted on this thread, sent a tech support request over a week ago for the exact same problem and has not heard from support. 
 
Some with 8.1 are working OK and some are not.  I don't know how many of those that are working OK have the 64 bit version installed.  As I've previously noted the 32 bit version installs and works OK.  I have two Windows 8.1 systems (totally different hardware) that have the exact same problem - one with X3b and the other with X2.
 
 
EDIT:  I looked at the list of fixes/enhancements in X3c and there is NOTHING mentioned about Windows 8.1, as has been suggested on here and other web sites.

FIXED! 
 
I had tried this, or something similar, before from a link I found doing a google search but it didn't work.
 
I found this on the Windows 7 forum, on a link that people with Adobe Photoshop were having the exact same problem with the "MSVCR110.DLL"  error and program not starting.  One of the posted responses with a link (shown below) was the fix.  I tried it with Sonar X3 and Windows 8.1 and it fixed it.  However, MSVCR110.DLL was already in the correct Windows folders, but apparently was corrupted. 
 
Here was the posted fix:
 
"GOTO:
Download Visual C++ Redistributable for Visual Studio 2012 Update 3 from Official Microsoft Download Center

I updated with the "VSU3\vcredist_x64.exe" file.
Shut down / Restart / CS6 loaded with the Nik plugin intact and no errors.

MSVCP110.dll is now in my C:\Windows\System32 folder."
 

Good to hear you got it fixed!    Having come across similar c++ redistributable issues at work I was fairly sure it was the file itself, but I've never come across a situation where the right version in the right location just didn't work.    Good to know.