Aardvark does not currently have WDM drivers, which is what Sonar defaults to use. In Sonar, go to Options - Audio - Advanced, and check the box that says "Always use MME interface..." and restart Sonar.

If you are using Windows 2000 or XP, as of 4/8/02, you need to make sure you've downloaded the full release of the drivers for the Aardvark at www.aardvark-pro.com