Saving widget gets an undefined variable

I am willing to be that since you have not initialized the widgets pool it cannot be duplicated.

So within your main class or plugin file you would add this:

For Class:

add_action ( 'widgets_init', array (
    &$this,
    'my_widgets' 
) );

For .php file

add_action ( 'widgets_init', 'my_widgets');

then create your function

public function my_widgets(){
    register_widget ( 'CachedFeed' );
}

Of course don’t forget to include your widget class.