VS-100 ....Has worked flawlessly until after the update.  Recording playback does not work consistently on newer recorded tracks. Playback on previous tracks work 8-10 times before having to restart SPLAT.  Still happening tonight as I am trying to determine issue.  Thanks for the reply.

I had this.....
 
Check to see what else is using the drivers, in my case after going into the windows mixer I could see my MOTU card had a mix return device which was hogging the driver, now this previously worked and worked with other programs but Sonar didnt like it so I disabled it in device manager and got everything working.
 
If you go into control panel and sounds, select playback device and advanced and then try and change the format does windows warn you that its in use?

Finally got some time to get back to this : turns out uninstalling and re-installing the Octacapture drivers did the trick. Thanks to everyone who commented.

Turns out I was premature in my previous posting : the re-installation of the drivers worked for exactly one session after the process - the next day I received the same 'Unable to locate audio device' message on the identical handful of tracks that first exhibited the issue. As before, numerous tracks with very similar structures work fine, it seems entirely arbitrary.
 
I notice in reviewing posts going back for some time that the Octa Capture seems to have ongoing issues : can anyone out there recommend a reliable USB interface that can handle Sonar's constant updating and erratic behavior?      

If you go into control panel and sounds, select playback device and advanced and then try and change the format does windows warn you that its in use?
 
This will help define whether its an issue with Sonar or Windows.

I have been experiencing the same issues for some time now. I have the VS-700 setup and I'm running Windows 10 64-bit (so had to apply the driver hack to get it working). The only way I can get the system to be stable is to use WDM drivers or ASIO4ALL.