Get Component isn't working too well

Hello again Unity Community;

I am creating my first game (not following any tutorials and etc.) and I seem to have difficulties with the command:
GetComponent<>;

Down bellow is the section of the code where I worked on the command:

			if (i == 2) {
				GetComponent<WPmsslCTRL> ().parabolCtrl();
				i = 0;
			}
		}

Which should run the the function:

	public void parabolCtrl() 
	{
		for (x = -50 ; x <= 50; x++) 
		{
			waypointNum.Add (Instantiate (wayPoint, new Vector3 (x,- (0.09f)*(x*x)+10, 0), Quaternion.identity)); // just like y= ax^2 + bx + c

		} 
	}

Unfortunately, I keep getting this error:

NullReferenceException: Object reference not set to an instance of an object
testSpawn.Update () (at Assets/Script/testSpawn.cs:58)

I made sure that the component is attached to a game object and both the component and the game object are set active. I am not clear on the issue with my getComponent.

if the WPmsslCTRL component is attached to a different gameobject (different than the gameobject this script is attached to), than you need to reference that gameobject and only then reference the WPmsslCTRL component:

public GameObject go;

 void YourFunction()
 {
        WPmsslCTRL _ctrl =  go.GetComponent<WPmsslCTRL> ();
        if(_ctrl != null)
         {
                _ctrl.parabolCtrl();
         }
 }