Can any one help I keep getting this error :

Assets/Standard Assets/2D/Scripts/Platformer2DUserControl.cs(3,27): error CS0234: The type or namespace name CrossPlatformInput' does not exist in the namespace UnityStandardAssets’. Are you missing an assembly reference?

using System;
using UnityEngine;
using UnityStandardAssets.CrossPlatformInput;

namespace UnityStandardAssets._2D
{
[RequireComponent(typeof (PlatformerCharacter2D))]
public class Platformer2DUserControl : MonoBehaviour
{
private PlatformerCharacter2D m_Character;
private bool m_Jump;

    private void Awake()
    {
        m_Character = GetComponent<PlatformerCharacter2D>();
    }

    private void Update()
    {
        if (!m_Jump)
        {
            // Read the jump input in Update so button presses aren't missed.
            m_Jump = CrossPlatformInputManager.GetButtonDown("Jump");
        }
    }

    private void FixedUpdate()
    {
        // Read the inputs.
        bool crouch = Input.GetKey(KeyCode.LeftControl);
        float h = CrossPlatformInputManager.GetAxis("Horizontal");
        // Pass all parameters to the character control script.
        m_Character.Move(h, crouch, m_Jump);
        m_Jump = false;
    }
}

}

Top of Script:

using System;
using UnityEngine;
using UnityStandardAssets.CrossPlatformInput;

namespace UnityStandardAssets._2D
{
[RequireComponent(typeof (PlatformerCharacter2D))]
public class Platformer2DUserControl : MonoBehaviour
{
private PlatformerCharacter2D m_Character;
private bool m_Jump;