Assets/vb_anim.cs(7,14): error CS0535: `vbButton' does not implement interface member

Hi all, I have a problem with my unity script. I'm trying to make a virtual button so I can rotate my cube. I have an error popping up and I just don't know how to fix this. First I thought it was some kind of spelling error but that does not seem to be the case I think... Any ideas? This is my code:

using System; using System.Collections; using System.Collections.Generic; using UnityEngine; using Vuforia;

public class vbButton : MonoBehaviour, IVirtualButtonEventHandler {

 public GameObject vbBtnObj;
 public Animator cubeAni;

 // Use this for initialization
 void Start()
 {
     vbBtnObj = GameObject.Find("LacieBtn");
     vbBtnObj.GetComponent<VirtualButtonBehaviour>().RegisterEventHandler(this);
     cubeAni.GetComponent<Animator>();
 }

 public void OnButtonPressed(VirtualButtonBehaviour vb)
 {
     cubeAni.Play("cube_animation");
     Debug.Log("Button Pressed");
 }

 public void OnButtonReleased(VirtualButtonBehaviour vb)
 {
     cubeAni.Play("none");
     Debug.Log("Button Released");
 }

}