Why this script doesn't work? (Disable Component)

Hello,
I want to make C# script that will disable walking on “J” key but it doesn’t work.

private FirstPersonController FPS; ------ is underlined on red color
and
FPS = GetComponent<FirstPersonController>(); is underlined too.

using UnityEngine;
using System.Collections;

public class Chodzenie : MonoBehaviour
{
    private FirstPersonController FPS;

    void Start()
    {
        FPS = GetComponent<FirstPersonController>();
    }


    void Update()
    {
        if (Input.GetKeyDown(KeyCode.J))
        {
            FPS.enabled = false;
        }
    }
}

Thank you for help!

The FirstPersonController class belongs to the namespace: “UnityStandardAssets.Characters.FirstPerson”

It allows you to access FirstPersonController:

 using UnityStandardAssets.Characters.FirstPerson;