Getting an Exception on Endless Runner 3D game

I referred to the tutorial series of: [Catlike Coding][1]

Situation: I am trying to implement Endless runner 3D game by referring the above tutorial. What happened is that when i implemented PlatformManager script, it says

InvalidOperationException: Operation is not valid due to the current state of the object System.Collections.Generic.Queue`1[UnityEngine.Transform].Peek () PlatformManager.Update () (at Assets/Platform/PlatformManager.cs:35)

There is a simple object pooling going on here,I searched google for days and couldn't find the answer. here is the PlatformManager.cs script:

 using UnityEngine;
 using System.Collections;
 using System.Collections.Generic;
 
 public class PlatformManager  : MonoBehaviour {
     public Transform prefab;
     public int numberOfObjects;
     public float recycleOffset;
     public Vector3 startPosition;
     public Vector3 minSize, maxSize,minGap, maxGap;
     public float minY, maxY;
     private Vector3 nextPosition;
     private Queue<Transform> objectQueue;
 
     void Start () {
         objectQueue = new Queue<Transform>(numberOfObjects);
         for (int i = 0; i < numberOfObjects; i++) {
             objectQueue.Enqueue((Transform)Instantiate(prefab));
         }
         nextPosition = startPosition;
         for (int i = 0; i < numberOfObjects; i++) {
             Transform o = (Transform)Instantiate(prefab);
             o.localPosition = nextPosition;
             nextPosition.x += o.localScale.x;
             objectQueue.Enqueue(o);
         }
     }
     void Update () {
         if (objectQueue.Peek().localPosition.x + recycleOffset < Runner.distanceTraveled) {
             Transform o = objectQueue.Dequeue();
             o.localPosition = nextPosition;
             nextPosition.x += o.localScale.x;
             objectQueue.Enqueue(o);
             Recycle();
         }
     }
     private void Recycle () {
     Vector3 scale = new Vector3(
             Random.Range(minSize.x, maxSize.x),
             Random.Range(minSize.y, maxSize.y),
             Random.Range(minSize.z, maxSize.z));
         Vector3 position = nextPosition;
         position.x += scale.x * 0.5f;
         position.y += scale.y * 0.5f;
         Transform o = objectQueue.Dequeue();
         o.localScale = scale;
         o.localPosition = position;
         nextPosition.x += scale.x;
         objectQueue.Enqueue(o);
         
         nextPosition += new Vector3(
             Random.Range(minGap.x, maxGap.x) + scale.x,
             Random.Range(minGap.y, maxGap.y),
             Random.Range(minGap.z, maxGap.z));
 
         if(nextPosition.y < minY){
             nextPosition.y = minY + maxGap.y;
         }
         else if(nextPosition.y > maxY){
             nextPosition.y = maxY - maxGap.y;
         }
     }
 }

How can i get rid of this error? Thanks in advance. [1]: http://catlikecoding.com/unity/tutorials/runner/