Hello Forums,
 
Was digging around for a similar problem but mine seems to be semi unique.
 
I recently had to reinstall a bunch of things. Long story short, when I open an old file, I get "Unable to Open Audio Playback Device blah blah blah". 
 
However, creating a new file or opening other projects work in one way or another. 
 
Does anyone know why this might be? Any possible solutions?
 
Running ASIO with ProjectMix I/O. 
 
WDM doesn't seem to work either.
 
.C

I saw this once ages ago when I'd (inadevertently!) recorded at 22.05KHz rather than 44.1 and the newer interface didn't like 22.05 - worth checking that.

I recently had to reinstall a bunch of things. Long story short, when I open an old file, I get "Unable to Open Audio Playback Device blah blah blah".

 
1. Make sure you installed the latest drivers for your OS
2. Make sure the sound card /interface is defined correctly inside sonar.
3. Maybe you can list all the individual settings for your sound crad. This way we can look and tell you what you mis-configured or did not configure
 
CJ