prefabs break movement scripts,

,I'm doing the Create With Code tutorials and working on my prototype, and I got everything working well- enemies chasing player, player dying dramatically, lots of good stuff. BUT. When I make my enemies and player into prefabs, my enemy movement goes nuts. It's the same script that's on those chasing balls from the 4th week, basically, and it works fine until I change everything into prefabs. Any help would be appreciated- I'm stuck! Here's my enemy controller.

private float speed = 5.0f;

 private Rigidbody enemyObjectRb;
 public GameObject player;

 void Start()
 {
     enemyObjectRb = GetComponent<Rigidbody>();
 }

 void Update()
 {
     enemyObjectRb.AddForce((player.transform.position-transform.position).normalized *speed);
 }

I think it's something about how it references the player gameobject, because it works fine in the scene until I make them prefabs, then it loses the unity reference to the player in my enemyController script. I have to drag the player gameobject in to the scripts in the Unity inspector again. But then my movement goes nuts! The enemies fly all over the place and never hit the player. What the heck? Does anyone know? I'd sooo love an answer.