X1c update....now no sound

Open up a project, it opens and now just a buzzing sound. If I press play a error message displays "Unable to open playback device. Device may not support the current projects audio format or may be in use".
 
In edit - preferences , my soundcard is displayed and set as playback still, so no issues there. Sometimes if I re-apply the audiocard in the settings I get playback, but if I close Sonar and reopen later the same problem.
 
Any ideas please.
 
Windows 7 64 bit
Native Instruments soundcard