Sometimes when Sonar X2 has issues the sound card turns off and you have to turn off the computer and then restart in order to use ASIO. Then you have to go through the whole process of waiting on your computer to reboot. Well that is not the case...most of the time. Instead try this and save time. 
 
Windows 7
Got to your Start menu . Look to your right you should see the name of your computer, documents, pictures music. Below that it says computer. 
 
Hover over computer and right click. A small menu will appear select manage. 
Then select Device Management 
Go to Sound, video and game controllers 
Go to your sound card device. 
Hover over it and select disable. Once it has been disabled re-enable it. 
 
You can now use ASIO again 
 
 

Good info! For external devices power cycle (off on)

Great tip! Why didn't I know this the other day when I rebooted... thx!

I've also had some success with just logging off, and logging in again when my soundcard locks up (doesn't always work depending on what caused it)
Thanks for this, I'll try your method next time and see if it helps.

That's a good workaround. I just close X2 and open it again. But my issue is when I accdentally try to playback in X2 while an audio player is still conected to the audio file. After that I see the warning messages.