Targetting Script Errors

Currently getting the following errors for my script:

NullReferenceException: Object reference not set to an instance of an object

Targetting.SelectTarget () (at Assets/Targetting.cs:64) Targetting.TargetEnemy () (at Assets/Targetting.cs:57) Targetting.Update () (at Assets/Targetting.cs:76) Targetting Script:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 using System.Collections.Generic;
 
 public class Targetting : MonoBehaviour {

 public enemyHealth eHealth;
 public GameObject enemy;
 public List<Transform> targets;
 public Transform selectedTarget;
 public string targetTag = "Enemy";
 private Transform myTransform;

     //Use this for initialization
     void Start () {
         targets = new List<Transform>();
         selectedTarget = null;
         myTransform = transform;        
         AddAllEnemies();
     }
     
     public void AddAllEnemies()    {
         GameObject[] go = GameObject.FindGameObjectsWithTag(targetTag);        
         foreach(GameObject enemy in go)    {
             AddTarget(enemy.transform);
         }
     }
     
     public void AddTarget(Transform enemy) {
         targets.Add(enemy);
     }
 
     private void SortTargetsByDistance() {
         targets.RemoveAll(target => target == null);
         targets.Sort(delegate(Transform t1, Transform t2) { 
             return (Vector3.Distance(t1.position, myTransform.position).CompareTo)
                 (Vector3.Distance(t2.position, myTransform.position));
         });
     }
     
     private void TargetEnemy() {
         if(selectedTarget == null) {
             SortTargetsByDistance();
             selectedTarget = targets[0];
         } else {
             int index = targets.IndexOf(selectedTarget);    
             if (index < targets.Count -1) {
                 index++;
             } else {
                 index = 0;    
             }
 
             DeselectTarget();
             selectedTarget = targets[index];
         }
         SelectTarget ();
     }
 
     private void SelectTarget() {
         selectedTarget.GetComponent<Renderer> ().material.color = Color.red;
 
         enemyHealth eh = (enemyHealth)GetComponent("enemyHealth");
         eh.target = selectedTarget.gameObject;
     }
     
     private void DeselectTarget() {
         selectedTarget.GetComponent<Renderer>().material.color = Color.blue;
         selectedTarget = null;
     }
         
     //Update is called once per frame
     void Update () 
     {
         if (Input.GetKeyDown (KeyCode.Tab)) {
             TargetEnemy ();
         }
     }
 }

and in my enemyHealth: I get the following Errors:

Assets/enemyHealth.cs(91,49): error CS0029: Cannot implicitly convert type UnityEngine.Transform' to Targetting'

 void Update() {
         
         hitChance = Random.Range (1, 100); // Generates a Random Number each time between 1 and 100
         
         if (Input.GetKeyDown (KeyCode.Alpha1)) {
                 Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition); 
                 RaycastHit hit; 
                 if (Physics.Raycast (ray, out hit, 100)) { 
                     if (hit.collider.gameObject.tag == "Enemy") { 
                         selectedTarget = hit.collider.gameObject.transform;
                         MeleeHit ();
                         MHCD = Time.time;
                     }
                 }
             }