I'm having an irritating issue and it might just be a limitation of ASIO + Windows, but:
 
Every once in a while as I move between programs I won't be able to hear any audio anymore. It usually happens if I get up and leave my computer for a few minutes, but not always. And sometimes even when I leave for a while this happens. The fix has generally been to reset my interface.
 
When I have SONAR open I can't have any other audio programs open or it won't play audio at all either.
 
I realize it's bad practice use your personal computer (the one that you web surf and play games on) for your audio machine, but it's the only one I've got.

Do you have an onboard sound card and an interface? What interface is it? Also try googling 'forum.cakewalk share drivers with other programs' or 'forum.cakewalk share with other audio'. That should bring up similar posts about this problem.

You may need to set sonar to share or set one of the interfaces as the default in windows. Have a read in the absence of any other help at the moment. Some interfaces simply don't share but most do even if it takes a setting change here or there.

call steinberg !!
 
lol 
 
more seriously , just use different driver , asio can't be shared , sonar has an option to allow other programm to use it anyway but not a great thing so just do this :
 
Sonar  : use  ouput 1/2
Sotware use output 3/4 
 
....  ect be sure to not selected 3/4 as active in sonar , depends on other programm but if it's just like windows media player or some like this , just use on board soundcard (just select it in windows as default)
 

It usually happens if I get up and leave my computer for a few minutes, but not always. And sometimes even when I leave for a while this happens. The fix has generally been to reset my interface.

If your interface is connected via USB, it's possible your USB ports are being powered down after a period of inactivity. Your symptoms describe that scenario to the letter.
 
Go into Device Manager, find the entries (there'll likely be more than one) labeled "USB Root Hub", open their property pages, and un-check the "allow the computer to turn off this device to save power" option. This'll prevent the USB ports from going to sleep and disconnecting from the driver.

I have the same problem with my Layla3G.  I can only open one audio program at a time...or specifically the one that is opened first, is the only one that will play.  I've messed with the "share programs" etc.   Never had success.
It's nice to listen to a YouTube or a MP3 without importing into Sonar, WHILE Sonar is open...  I like to get ideas, comparisons, etc.
The Layla is a PCI interface and I have just a built in one on the motherboard....which would be fine for simple playback.  Since I can't get two to work at once (or Sonar plus anything else) , I typically just disable the cheapie one on the motherboard.
 
Interested in hearing solutions as well.

I thought it might be USB suspending so I disabled that on all of my USB ports in device manager but it didn't change anything.
 
I have the onboard audio disabled, and am using an M-audio Fast Track Pro as my interface. 
 
I hadn't tried clicking the "share this device" box before so I'll try that.
 
The strange thing is even if I don't use Sonar, sometimes when I move between different programs I'll stop being able to hear any audio and have to reset the interface.

Re-install M-audio drivers or check their forums for anything similar.

Years ago I had an MAudio Soundcard that did something similar - the only answer I found was to change to a better make - nearly everything I've ever had from MAudio has been a problem or gone wrong at some time or another so they are one Company I will never purchase from again, ever!
Last (and final for me) problem were three Mid Air Keyboards - all went wrong, all tried to be repaired a couple of times then no one would touch them and then they were withdrawn from sale. Shame as when they worked they were really good - just TOTALLY unreliable!!
Nigel
 
 

Tried reinstalling the driver but that didn't help.
 
Just a few minutes ago I had VLC media player open playing a music file, then I paused it and left the room, came back less than 10 minutes later and had to reset my interface in order to play audio.

Since you've already disabled the USB power-down option, you can probably assume it's not the USB port, especially if other USB devices appear to not be affected. Now you have to consider the rest of the chain: the audio interface and cable. A flaky cable can certainly do it. My own interface will do it on a very hot day after running for several hours.
 
Anybody suggested checking for IRQ conflicts yet? Not a high probability, especially if this problem just started, but worth looking into anyway. Also, does it happen with all other USB devices disconnected?