I took some time off from recording and just got back to it.  One of my projects won't play (the others seem fine) and I get this prompt:  "Unable to open audio playback device.  Device may not support the current project's audio format or may be in use."
 
When I go into preferences, all the settings are the same as the projects that I can open so I'm at a loss here.
 
Any ideas/tips?  Thanks!

Not sure if your tried this, but check to see which outputs each of your audio tracks and buses buses and tracks are assigned to.  This is done on the tracks and buses themselves, not in Preferences

Hi. I agree with BRainbow.
Check that none of your tracks or buses gets routed (by accident) to your internal sound card (as an example).
You're using ASIO drivers, I presume?
All the best.

Thanks guys.  I did not think of that so I'll try it later.  I hadn't been recording recently and now it does seem like some of my settings have been altered due to the various updates w/ Windows and my audio interface.  Hopefully that's the ticket.  Thanks again!

I figured it out...  The project I couldn't open used a different sample rate than all the other projects.  Once I figured that out and made the change, it worked.

I found..when Sonar lost my audio driver upon opening up sonar...once restarting sonar , i had to go into preferences, unselect the asio driver, hit ok, and reselect it..hit ok...all was ok for a while...
 
As said above, sometimes rerouting occurs of sends/ main outputs, causing no audio playback, but vu's were showing to be playing...so, never really solved this, as to why....but,...
 
I believe it is a OS issue more and more using internet services, and sending out the dirty laundry to , by Bing calling up services of internet, and or tied to audio devices.
 
Again I believe....because Bing calls explorer...and when setting up for the first time the MB drivers...OS pegs defaults to, and for updates, and third party data collection through, drivers first put into play....if a service of audio is installed first as onboard audio when running motherboard drivers, to install windows upon to get all up to snuff and running...It might be held for defaults, to use for to gain, when doing the spy and send data via...the drivers get muddled up...by that process.
 
Again, I believe...only because I watched my ports , and bing was behind that usage of sending out through ports.
 
As I do not use edge or internet explorer, of which bing is the search engine of? ..supposedly for MS ...And not the default I setup...but seems to be running services behind the vale of cloaked muse, to gain data, and send out data...what is new written to HD.......You, as I have, might assume together, is behind some of the cause..messing up those all important routings of audio devices.
 
hope someone, or something posted helps.
 
Cheers!

I get this on my current Roland Octa-Capture with all projects I recorded using my old (Allen & Heath Zed10) sound interface..
Changing from ASIO to WDM lets me continue. (With much degraded performance)

Please edit your first post, by amending the thread title to include (Solved) so people nomthe status of the issue.