CS0120 - Object reference required but it's already assigned.

New to Unity here. I'm having some issues with a script.

I'm trying to find the x,y and z coordinates of a GameObject and logging them. I have this script for that:

 public GameObject mrh;

 // Use this for initialization
 void Start () {
     Debug.Log(mrh.transform.position.x.ToString());

     _header = new[] {
         "TimeStamp",
         "BoxCount",
         "Right Hand x",
         "Right Hand y",
         "Right Hand z"
     };
 }

 public static void UpdateData()
 {
     _data[2] = mrh.transform.position.x.ToString ();

(I erased the parts that don't matter).

Here's the thing. I wrote a different script that also needs GameObjects

 public class ShowEndPanel : MonoBehaviour {
 
     public GameObject SimulationPanel;
     public GameObject EndPanel;
     private double auxTime;
 
     public Text nameText;
     public Text scoreText;
 
     // Use this for initialization
     void Start () {
         EndPanel.SetActive (false);
     }
 
     // Update is called once per frame
     void Update () {
         auxTime = TimerScript.getTimeLeft ();
         if (auxTime <= 0) {
             UpdatePanelText ();
             SimulationPanel.SetActive (false);
             EndPanel.SetActive (true);
         }
        }

The bottom script works fine, the top one doesn't. I already dragged the object i want to the script, and it's working for the Debug.Log but as soon i uncomment the _data[2] line in UpdateData() i get the CS0120 error. Any ideas?

The Objects assigned: