I don't know if anybody ever responded with a viable answer to this and since I had the EXACT SAME problem, I thought I would toss out my answer.
I'm still not exactly sure WHY it happens, although I believe it has something to do with that useless Conexant SmartAudio app that loads with the driver, trying to take exclusive control while sonar is using it. So.....
With that in mind, I uninstalled the Conexant Pro Audio Device from Add/Remove Programs in control panel. (which, of course, uninstalls the sound driver, but, also uninstalls that SmartAudio control app)
Then,
Instead of reinstalling the software, I just right click on "Computer", goto properties, device manager and search for changes... The sound card will then pop back into the device list, with a yellow exclamation point. then, you just right click and re-install the drivers by doing it "automatically" and allowing it to search online for the driver. Once the driver is installed, the sound card will work perfect with windows again, but, you will be minus that useless SmartAudio app that comes with it, and.... you will also be rid of the annoying pop up in sonar.
so...
As long as you can live without that useless SmartAudio app....
there it is.
Good luck!