UnityException: You are not allowed to call this function when declaring a variable. Move it to the line after without a variable declaration.

I’m having a problem that is driving me insane. I’ve debugged the script manually and could not find the problem. The error that I am getting is this:

UnityException: You are not allowed to call this function when declaring a variable.
Move it to the line after without a variable declaration.

And the code:
using UnityEngine;
using System.Collections;

public class UIController : MonoBehaviour {
	public GameObject player;
	private PlayerBehaviour playerScript;

	void Start () {
		player = GameObject.Find ("Player");
		playerScript = player.GetComponent<PlayerBehaviour>();
		Debug.Log (playerScript.health);
	}

	// Update is called once per frame
	void Update () {

	}
}

Try moving the line:

player = GameObject.Find ("Player");

to Awake() method;