Virtual Button problem

Hi i just recently started using Vuforia sdk and i have difficulties making virtual buttons ...i must say at the beggining that i tryed the sample app and well did not understand it ;/ 

here is what i did:i added virtual button to the scene as a child of image targer then added plane as a child of virtual button so i can see it . Then i have written simple script to manage button actions and added that script to image targer.

public class ManageButtons : MonoBehaviour, IVirtualButtonEventHandler {

    // Use this for initialization    
    void Start () {
        
        VirtualButtonBehaviour[] vbs = GetComponentsInChildren<VirtualButtonBehaviour>();

        foreach (VirtualButtonBehaviour item in vbs) {            
            item.RegisterEventHandler(this);            
        }        
    }

    // Update is called once per frame    
    void Update () {
    }

    public void OnButtonPressed(VirtualButtonAbstractBehaviour vb) {        
        Debug.Log("Helllllloooooooooo");        
    }
    
    public void OnButtonReleased(VirtualButtonAbstractBehaviour vb) {        
        Debug.Log("Goooooodbyeeee");        
    }
}

and it's not working ;/ can anyone indicate me to a solution