no audiosource attached

MissingComponentException: There is no ‘AudioSource’ attached to the “SettingsContainer” game object, but a script is trying to access it.
You probably need to add a AudioSource to the game object “SettingsContainer”. Or your script needs to check if the component is attached before using it.
ToneSliderScript.Update () (at Assets/Scripts/ToneSliderScript.cs:18)

The attachment below clearly shows the AudioSource is attached. What am I doing wrong?

102840-capture.jpg

No, that image shows that an AudioSource is a child of SettingsContainer. You need it to be a component of SettingsContainer.

You can do so by selecting the SettingsContainer object, clicking Add Component, then choose an Audio Source component.