I have had consistent success using the Zoom R24, both as an audio interface and as a control surface with a couple of versions of Sonar (8.5 and X2); both on an older machine running XP and my new, home-brew core i7 machine running windows 8.1.
 
However, about a month ago, only one feature of the Zoom R24 stopped working with Sonar; the faders no longer control the on-screen faders of Sonar X2 (X2a 64 bit to be exact...the patch has been installed).  The faders in Sonar do not respond to faders of the Zoom R24.
 
The Zoom R24 still works perfectly as an audio interface.  The solo/mute/record buttons all work fine.  The transport controls and jog wheel work perfectly.  The only aspect missing is fader control.
 
I tried using the Zoom R24 with Reaper, and the fader controls work perfectly with Reaper; also every other control works perfectly with Reaper and the Zoom R24.
 
Here are the steps I have taken trying to fix the problem:
 
1. Uninstalled Sonar completely, shut down, restarted, reinstalled Sonar (TWICE!)
2. Uninstalled Zoom R24 driver, (the latest 64 bit version), shut down and reinstalled (twice, both times checking the Sonar checkbox)
3. "Repaired" windows 8.1 with the installation disk (not sure what I did here, but it was NOT a complete reinstall of windows; no damage done, I don't think)
3. Read everything I could find online about this problem; I was unsuccessful in finding anything about loss of fader control
 
The fact that R24 faders successfully control Reaper, and that Sonar faders do not respond to R24 faders, seem to indicate that Sonar is at fault.  (I do not use Reaper, but installed it to test the Zoom R24).  (BTW, all other control functions of the R24 work fine with Reaper as well.)
 
When reinstalling Sonar, I did try to get the faders to respond to the R24, before and after installing the X2a patch; no success; faders did not respond in either case.
 
I've been using Cakewalk since 1998, from Guitar Tracks (as a beta tester), pro audio and now Sonar.  Every problem with Sonar, I was able to find something in a forum somewhere that helped me solve it.  This is the first time I have not seen a similar problem online.  I really could use help on this, please!
 
I love the ability to draw volume, pan and other controllers with the physical fader on the R24, and I'm bummed now that I cannot.  Budget won't allow any purchases right now (of another controller, for example).
 
I would love to hear your feedback.  Thank you!
 
BeGroovEye
Asrock Z87 extreme4 (onboard Realtek audio interface, latest drivers)
Intel core i7 3.5 ghz (not overclocked)
Windows 8.1 (purchased at MicroCenter)
8 gb ram
seagate 2tb hdd
Zoom R24
M-Audio Oxygen 8
Motu Fastlane midi interface
Tripp Lite isobar ultra x4
 

BTW windows 8.1 64 bit

Upgrading to Windows 10 fixed everything.