Anyone encountered this error:
"Unable to open audio record device.  Device may not support the current project's audio format or may be in use." and then this message "The above Audio/MIDI device was disconnected from your system.  Would you like SONAR to reroute these outputs to an available device?....".  I'm using Platinum, and this suddenly started on a few projects.  Some projects open, some I get these error messages.  What gives?
Bob

Note, this happens when I press the transport PLAY button.  However, some projects play fine, others don't.

rename the aud.ini to aud.old or something that corresponds to your version of SONAR and start SONAR.
See if your troubles persist.

You don't say what your interface is or what driver mode, But this issue is very commong when other audio drivers exist on a computer and the "good" driver gets kicked out becuase the "other" driver is trying to rule the roost. 
Asio4all is one of them. On new machines your HDMI audio driver often needs to be disabled. 
Then even the simple on board audio drivers can cause this to happen but this is uncommon.
The other nasty driver is anything by Creative labs ( sound blaster) 
 
The other cause can be using the wrong USB port. 
Changing ports used to install the driver should be avoided
Using USB 3 ports ( blue) often cause issues. 
Disable USB suspend in Power settings advanced. 
 

 Thanks all for suggestions.  I'll try renaming the aud.ini file.  I'm using an RME Fireface 800 interface, and have for years with a Firewire connection to the computer.  Absolutely no changes to the system in a while.  Feels like corrupt files issue, Win update interference, etc. as it is quite sudden.

Yes Windows 10 updates have not been kind to people around here lately. 
If there was one thing that would make life better with windows 10, it's the return of the old choices you had before so we could " Let Windows tell you when there are updates available but let you choose when to download and install"  
Or at least a pop up balloon to warn that your computer is updating and why it's screwing up. Or reboot without warning when your in the middle of a 12 GB download...

This issue mysteriously disappeared today as quickly as it appeared a couple days ago.  Don't you hate that!  I'm blaming the issue on the user :)  Thanks all for your suggestions.
Bob