That may have once been the case but is no longer. Of 21 DLLs in that folder, 11 are ActiveX and require registration, specifically the Sonitus suite. I'd assume it was just a typo in the install script, but that doesn't explain why one user gets the message and others do not.

There are 2 different regsvr32.exe:
Under Windows 10 x64 you have to run the "%systemroot%\System32\regsvr32.exe"
And with Windows 10 x32 you have to run "%systemroot%\SysWoW64\regsvr32.exe"
Probably there is a wrong code in the installer.
 
Maybe this works 
Open a cmd box and go to the path of "multivoicechorusflanger.dll"
Then run        %systemroot%\System32\regsvr32.exe  multivoicechorusflanger.dll