Clarification about MY_Controller and relative inheritances

@Dave friend, have you tried to var_dump in Backend_Controller's constructor? I'm afraid its not loaded. or try to instantiate it in your class Dashboard which is basically loaded by magic router.

PHP Code:

class Dashboard extends MY_Controller
{
    public function index()
    {
        // If this returns an error then your Backend_Controller is not loaded
        $oBackend = new Backend_Controller();
    }
} 


You extend My_Controller to CI_Controller while Backend_Controller extends MY_Controller. I think you missed it my friend. No one extends or instantiate Backend_Controller so no chance to access it's instance, your Dashboard also extends to MY_Controller. In your structure MY_Controller stands as your base class neither Backend_Controller nor Frontend_Controller. That's why.

I think you're reading it wrong. Look at my code again.

1. MY_Controller extends CI_Controller;
   
2. Backend extends MY_Controller;
   
3. Welcome extends Backend;
   

I substituted "Welcome" for the OP's "Dashboard" cause I was too lazy to create another class.

The inheritance chain will instantiate Backend.

I know "Backend" was created because the object "river_m" is successfully used in "Welcome" to return data from the db.

In my example I did not define a Frontend class but if I did it would extend MY_Controller.