UnassignedReferenceException and Invalid Cast exception

In my script I keep on getting errors with UnassignedReferenceException and Invalid cast exceptions

The errors are

InvalidCastException: Cannot cast from source type to destination type. Obst1_Attack.obst1 () (at Assets/Standard Assets/resources/Obstacles/Obst1_Attack.cs:15) Obst1_Attack.Update () (at Assets/Standard Assets/resources/Obstacles/Obst1_Attack.cs:41)

UnassignedReferenceException: The variable Obstacle2 of Obst1_Attack has not been assigned. You probably need to assign the Obstacle2 variable of the Obst1_Attack script in the inspector. UnityEngine.Object.Internal_InstantiateSingle (UnityEngine.Object data, Vector3 pos, Quaternion rot) UnityEngine.Object.Instantiate (UnityEngine.Object original, Vector3 position, Quaternion rotation) Obst1_Attack.obst3 () (at Assets/Standard Assets/resources/Obstacles/Obst1_Attack.cs:27) Obst1_Attack.Update () (at Assets/Standard Assets/resources/Obstacles/Obst1_Attack.cs:45)

This is my code

 using UnityEngine;
 using System.Collections;
 
 public class Obst1_Attack : MonoBehaviour {
     // Use this for initialization
     void Start () {
     
     }
     public float speed = 10f;
     public GameObject Obstacle1_0;
     public GameObject Obstacle0;
     public GameObject Obstacle2;
     public bool Iscollision = false;
     void obst1 () {
         Rigidbody2D obst1Ingame = (Rigidbody2D) Instantiate(Obstacle1_0, transform.position, transform.rotation);
         while (Iscollision != false) {
             obst1Ingame.velocity = transform.forward * speed;
         }
     }
     void obst2 () {
         Rigidbody2D obst2Ingame = (Rigidbody2D) Instantiate(Obstacle0, transform.position, transform.rotation);
         while (Iscollision != false) {
             obst2Ingame.velocity = transform.forward * speed;
         }
     }
     void obst3 () {
         Rigidbody2D obst3Ingame = (Rigidbody2D) Instantiate(Obstacle2, transform.position, transform.rotation);
         while (Iscollision != false) {
             obst3Ingame.velocity = transform.forward * speed;
         }
     }
     void OnCollisionEnter(Collision collision) {
         ContactPoint contact = collision.contacts[0];
         Iscollision = true;
     }
     void Update() {
         float randomizer = Random.Range(0.0f, 1.0f);
         float randomizer2 = Random.Range (0f, 100f);
         if (randomizer2 < 44 && randomizer2 > 34) {
             if (randomizer <= 0.34 && randomizer >= 0.0) {
                 obst1 ();
             } else if (randomizer <= 0.67 && randomizer > 0.34) {
                 obst2 ();
             } else if (randomizer <= 1.0 && randomizer > 0.67) {
                 obst3 ();
             }
         }
     }
 }
 

I assigned the prefabs in the inspector but it still gives me the error.