TwangGuru
I've been having some similar crazy issues. S-Plat will open... and usually, will play my project. However... when I perform some action -- and pardon the vagueness -- I just haven't been able to pin down what action(s) initiate the issue. The issue is that playback stops -- no sound, no meter action, no nada. BUT... if I go to any arbitrary track and change the INPUT source (say to scarlett 18i20 3 from scarlett 18i10 1... then there is a POP and the playback comes back. Usually, that is. I have to say this really eats into productivity, creativity and just general frame of mind.
 
So... I'm going to try with "Share Drivers with other programs" to see what happens. I will post back... and thanks, as always, to other Sonar users willing to take time to help others.

Try...
With mix control do a full uninstall, reboot, install (latest from internet), then reset everything in mix control. Set it up then save to hardware.
 
If you have ASIO4ALL installed anywhere remove it.

Nope... checking the "share drivers" box did not fix it. It's clearly some driver issue in my case. I've updated to the latest Scarlett drivers, all is patched in S-Plat to "Hopkinton"... my computer is a beast -- Intel(R) Core(TM) i7-4930K CPU @ 3.40GHz, 3401 Mhz, 6 Core(s), 12 Logical Processor(s), 16GB Ram, 1TB SSD primary drive, 500GB SSD Data drive, Win 7/64 Pro all updated, Kaspersky AV (and, yes, I've tried shutting it off). There are no errors shown in the event log... no driver crashes. Just now, it did this trick when I "Bounced to Tracks" for a listening mix... shut off audio, but when I changed the input of Track 1 (Kick Drum), all came back. This is driving me crazy!!! One more VERY strange thing - the SPACE bar is not starting/stopping playback occasionally... also, very irritating!!!
 

Doktor Avalanche
Try...
With mix control do a full uninstall, reboot, install (latest from internet), then reset everything in mix control. Set it up then save to hardware.
 
If you have ASIO4ALL installed anywhere remove it.

Thanks for the suggestion... I'll try it and let y'all know.

Hmmm, are any other applications running when it happens? The first thing that comes to mind off the top of my head is in the windows sound settings where you can select to allow applications to take control of the device. So, maybe check that box if it isn't already. Also, I have had problems using any other USB cord than the one that was provided - in case you were like me and tried to get a longer one.

This is a preliminary assessment but I finally succumbed to Microsoft's desire for me to upgrade to Windows 10. I had heard that it was good with multi-processor systems and handled drivers differently. So... away I went. I've tried several of the things that would kill the driver -- and safari, sagoodie...
 
My guess is that the Scarlett 18i20 is the culprit -- I think the driver and MixControl 1.8 was written for Win 8.1 and somehow violated the DDK rules for Win 7/64. I'm not going to look the gift horse, etc... I'm just enjoying some trouble free S-Plat use.
 
Thanks to all who offered suggestions and add my name to the list of pretty satisfied Win 10 upgrade recipients.
 

TwangGuru
 
My guess is that the Scarlett 18i20 is the culprit -- I think the driver and MixControl 1.8 was written for Win 8.1 and somehow violated the DDK rules for Win 7/64. I'm not going to look the gift horse, etc... I'm just enjoying some trouble free S-Plat use.

http://us.focusrite.com/answerbase/windows-10-compatibility
 
Should work well...
Says there are problems with the latest firmware update (what firmware are you on?). Focusrite don't say what the issue is with the firmware but I suspect it's just some have problems with the installer, when it is installed it should work fine (firmware is not OS specific). Anyway please let us know on post #21 when you are done. Thanks... 

I've now been working with the Scarlett 18i20 and S-Plat (now Ipswitch version) since my last post... no problems since I upgraded to Windows 10. There are a few things that irritate me about Windows 10, but it's FAST and certainly overcame the driver issues which I was experiencing with Win7/64. So add me to the "upgraded to Win 10/64 and happy I did" list.

Focusrite Support recommend to me to continue to use MixControl 1.8 with my Scarlett 18i20, rather than the beta 1.9 versions.
 

Thanks for the info