Hello,
I recently ungraded from Sonar X1 to X2. Now when I load a song I get the following message:
'Unable to open audio playback devices. Devices may not support the current project's audio format or may be in use.'
I never had this problem before. Is there any way to fix this without doing song all over?
Any help would be greatly appreciated. Thanks.
Michael Thierry

This can happen for a couple reasons. First, make sure the sample rate on the interface matches the intended sample rate in the project. Some interfaces will switch automatically, some won't.
 
Also try WDM instead of ASIO to see if that makes a difference. WDM can aggregate interfaces, so if another audio is doing something else in the system, it won't interfere with the device you're trying to sue with Sonar. This will also let you know if Sonar is seeing more than one device.
 
BTW my confidence in this advice is only about 60% but a least check these before trying other options.

I was thinking Sample rate too. Some ASIO devices will switch automatically but sometimes it won't. You will have to do it manually.