Something interfered with your SONAR installation. Try reinstalling SONAR but click NO anytime you're asked to restart the computer during the install process. You WILL need to restart after the installation has been completed.

If that doesn't fix the problem try this: Close all programs running in the background. Install DirectX 8.0a from Microsoft, then restart the PC. Next, reinstall SONAR. Do not restart the PC until the SONAR install has completed.