Since Manchester a number of previously fine projects simply will not play , full error message below. Seems to be totally hit and miss, many are still playing OK and there's no apparent common factor in the problem songs. Nothing but Manchester has changed on my PC (I7, Windows 10, eight core 16 GB RAM with an Octacapture).  Tried soloing and muting combinations of tracks with the same result.
 
Unable to open audio playback device. Device may not support the current project's audio format or may be in use. 

So you have verified the interface and driver mode settings in SONAR have not changed?

Thank you for your reply. Sonar updates have typically not changed any of my settings and I do not change them at all for particular projects. If it was an accidental change by the update, wouldn't all of my projects be affected?
I tried a random assortment of older projects and material as old as 2010, 2011,2012 plays back fine. The projects that won't play all use a mix of analog tracks and soft synths, and I have similar tracks recorded within the same time period that play without a hitch. One song I was doing a final mix on two days before Manchester now simply will not play, but a remix - based on the same original project - plays perfectly :  I've added no hardware, downloaded no Windows updates, and the Octacapture drivers are at their latest version.     

Perhaps there is a track in this particular project that has a resource hungry plugin?
You could try freezing any track(s) that have a lot of plugins or fx and see if it plays then (freeze first before you hit play)

Thank you. Many of the tracks are frozen already (I use Izotope 2, which is very resource-hungry). And I don't see why projects that were playing successfully a day or two before  - with the same synths and effects - suddenly won't play. But others with very similar configurations do. And this happens exactly after Manchester, seems too coincidental to be coincidental.

Noting similar issues with a setup using a Roland Quad Capture. Seeing this message at times when switching out of Sonar to check a clip on either FB or YT as well as loading a project. Running Manchester, use it every day and haven't run into it yet but the same issue observed with earlier releases.  
 
I initially thought it might have something to do with different project sample rates but that does not appear to be a factor in your case. I have "Share Drivers with other Programs" checked in Preferences which opens up another possible issue. Might be worth checking the Roland settings before you start Sonar, just to make sure nothing else has "influenced" them. 
 
I've been able to load and run the projects after some combination of close/restart Sonar, reboot the PC. 
 
The Roland drivers are a more likely suspect. I've had to reinstall them several times, perhaps as a result of a Win 10 update or a less than robust driver design. 
 
 

Interesting. This sounds very plausible because over the last number of Sonar updates I've encountered similar issues...for a while Sonar would 'lose' the sound card if I played anything through Windows Media Player while it was running. On a different update it would simply not play certain projects randomly, but there was no error message and restarting Sonar fixed it.  I haven't checked the 'Share Drivers with Other Programs' setting but I sure will now. Thanks and I will also reinstall Octacapture drivers. 

If you;re not able to get the project running after;
1) restarting Sonar,
2) restarting your PC,
then yes I would uninstall the Roland drivers and reinstall them. 
 

Very similar issue here also after the Manchester update, many of which are the same.  After the update, no audio playback after recording a track.  On opening preferences to make sure my settings did not change, I closed out of preferences (without changing a thing) and everything was back to working.  Did this multiple times and the same thing happened until I opened "Preferences" and closed back out of the window. After a few more times of this, audio does not come back and have to restart Sonar. Nothing even makes any sense to this.  I did update the Melodyne and now get multiple crashes which is another thread but wonder if this also has something to it. I do want to add that NOTHING has been changed in any setting or updates to WINDOWS except for Manchester update.

What audio interface are you using Bradley?