Try uninstalling and then reinstalling your interface drivers. If this doesn't work, try these:

1. Go to Start > Search > All Files and Folders > Type in "aud.ini;" Select all files that show up, right click on them, and press "Delete."
2. Sonar should now open and work properly.

If not:

3. Go to Start > Control Panel > System > Hardware > Device Manager > Sound, Video and Game Controllers; Disable all audio interface drivers.
4. Restart your computer.
5. Open Sonar.
6. Go to Options > Audio > Advanced; Set the drivers to ASIO mode, and check "Share drivers with other programs." Press "OK."
7. Go to Project > Clock Source; select "Audio."
8. Close Sonar, reenable your interface driver(s), and then restart your computer.
9. Sonar should now open and work properly.

If not:

10. Completely uninstall and remove all files from both the drivers and Sonar (including all shared files and plugins , registry files, and .
11. Reinstall your drivers first, then Sonar.
12. Sonar should now open and work properly.