you should be able to look in preferences/drivers and see the driver type you are using.
in this case it should be set to ASIO.
what i think is happening is your soundcard is somehow being disconnected each time you open sonar.
now this can happen for a few different reasons,driver conflict,crashes.
in thats same preference menu look in playback/your soundcard should have check marks next to it.
can you confirm this?
next time you open a project,before you click on preferences(or what your calling properties)take a look at your master fader in/out.
if its blank,than this will confirm your soundcard is lost apon start up.
once you confirm this we can move on to a solution.
Charlie