I'm amazed that SONAR apparently won't work with any kind of other audio thing opened at the same time....Using windows pro 64 bit and Focusrite Forte, same results with a Layla 3G for years. The 'share audio driver' is always checked. It amazes me I can have multiple MS explorer windows open with some kind of audio playing in them, and also have  both Microsoft media player and winamp and multiple youtube windows ...all running simultaneously no sweat, but the second even 1 other audio thing is opened while SONAR is, I get silence or a 'SONAR cannot play etc...check your settings,etc' ....... I called Cakewalk support, they told me to call Focusrite support! lol....
I can't really benefit from all the great Youtube Cakewalk tutorials on SONAR, nor keep media player open to hear commercial, mastered stuff to reference as I record/mix if I constantly have to close one or the other, SONAR or the YOUTUBE videos (if SONAR was opened  first, I can watch the video but no sound, if YOUTUBE was opened first, I get no sound and/or the error msg mentioned earlier)  and it's a major bummer. Does anyone have any suggestions? This should be very doable, but hasn't worked for years and years for me and why I was hesitant to upgrade.

You can only have one if you're using ASIO mode. Switch to WDM (or MME) and you can have more than one. However, you may have timinig issues if the two devices have different clock speeds. 

ASIO only allows a single program to use it.
 
My recommendation would be to pick up a cheap pair of computer speakers ($10-$30) and plug those in and make your on-board sound be the default sound device for Windows.
 
That will use your on-board sound card/chip (which will use WDM drivers) to play everything that is outside of Sonar, while at the same time allow Sonar to use the ASIO drivers of your audio interface.
 
Many many folks do as noted above, to get around the ASIO restriction, including me.
 
Bob Bone

thanks for the replies...is the latency with WDM as good and low as ASIO?

I wonder if this ASIO for all software will make it work....man, what an unnecessary PITA in this day and age!!

WDM is actually better but it all depends on the developer. ASIO is a Steinberg driver model. WDM is built into windows. ASIO isn't. If the developer does a good job in creating the driver WDM can out perform ASIO. In general people think ASIO is better but only because developers often put more effort into creating them. WDM is a huge driver model that is for all sorts of drivers. 

Got it working! Forte's tech support guy fixed this in about 45 seconds for me....changed back to ASIO in SONAR, with NO projects open, set to 24/96, then right clicked on the windows 8 speaker icon in the lower right , right click on playback devices, highlighted the Forte , and it setting on 2 channel 16 bit and I can hear audio now from a SONAR project and media player, you tube etc...not exactly sure what changed or if this will work again in the future but I'm a happy camper for now ..

another quick and easy solution: 
 
if you want to release the audio driver without quitting Sonar: 
 
Go to the Preferences menu; open the Audio setup page, 
stay on this page, open your other audio software, driver will be available. 
 
Sonar should take it back when closing the Preference menu. 
 
I've been doing this for years.. ;) 
 
Cheers ! 
 
V