I'm installing SONAR Artist on a Win10 laptop that's been reformatted.  Downloaded Command Center, etc.  Chose to "Install all" after clicking on SONAR Artist.  It was doing it's thing for a couple minutes when this error came up:
 

C:\Program Files\Cakewalk\Shared Plugins\multivoicechorusflanger.dll
Unable to register the DLL/OCX: RegSvr32 failed with exit code 0x3.
Click Retry to try again, Ignore to proceed anyway (not recommended),
or Abort to cancel installation.

 
So now what?
 
 
UPDATE:  This particular issue seemed to be related to the Classic Creative FX Suite.  I did nothing to resolve it right away, instead I went ahead and installed everything else (Rapture, CA-2A Leveling Amp, etc.).  Then I re-ran the FX Suite installation, and it went through no problem.

http://forum.cakewalk.com/Looking-for-users-who-had-the-DLL-issue-Please-add-your-info-m3675254.aspx
 
You are not alone, 
 
What version of Windows 10-- 1703 or 1709?
And are you using McAfee? 

http://www.cakewalk.com/Support/Knowledge-Base/2016000033/Unable-to-register-the-DLL-OCX-RegSvr32-failed-with-exit-code-0x3
 

Thanks guys, I did try the forum Search but it kept saying there were no records. ?
 
I'll look at those links right now....
 
 

Cactus Music
What version of Windows 10-- 1703 or 1709?
And are you using McAfee? 

 
 
1703, no McAfee (using Windows Defender)

(commented removed by me. I inserted it into my original post as an update.)

<geek alert>
Sigh, a downstream result of using a free setup tool that registers Dlls this way instead of using a Windows Installer-based setup. 
 

That DLL does not require registration.
 
C:\Program Files\Cakewalk\Shared Plugins>filever -v multivoicechorusflanger.dll
--a-- W32    DLL ENU        2.0.1.47 shp  1,025,536 12-30-2011 multivoicechorusflanger.dll
        Language        0x0409 (English (United States))
        CharSet         0x04b0 Unicode
        OleSelfRegister Disabled             <====
        CompanyName     Cakewalk, Inc.
        FileDescription Cakewalk Project5 Multivoice Chorus/Flanger
        InternalName
        OriginalFilenam
        ProductName     Project5
        ProductVersion  1.0
        FileVersion     2.0.1.47
        LegalCopyright  Copyright (c) 2003 Twelve Tone Systems, Inc. All rights reserved.

bitflipper
That DLL does not require registration.
 
C:\Program Files\Cakewalk\Shared Plugins>filever -v multivoicechorusflanger.dll
--a-- W32    DLL ENU        2.0.1.47 shp  1,025,536 12-30-2011 multivoicechorusflanger.dll
        Language        0x0409 (English (United States))
        CharSet         0x04b0 Unicode
        OleSelfRegister Disabled             <====
        CompanyName     Cakewalk, Inc.
        FileDescription Cakewalk Project5 Multivoice Chorus/Flanger
        InternalName
        OriginalFilenam
        ProductName     Project5
        ProductVersion  1.0
        FileVersion     2.0.1.47
        LegalCopyright  Copyright (c) 2003 Twelve Tone Systems, Inc. All rights reserved.

Then tell Cakewalk to stop running RegSvr32 on it!!!!!! 
 
"C:\Program Files\Cakewalk\Shared Plugins\multivoicechorusflanger.dll
Unable to register the DLL/OCX: RegSvr32 failed with exit code 0x3.
Click Retry to try again, Ignore to proceed anyway (not recommended),
or Abort to cancel installation."

It does actually export the canonical COM functions, no idea why the flag would not be set. 

All the plug-ins in "C:\Program Files\Cakewalk\Shared Plugins" are DX format and must be registered.