Unity错误:“；无法从源类型强制转换为目标类型“”；

我目前正在创建一个团结的游戏，如果我制作了它，那么游戏中的背景和障碍物就会不断"重生"并创建一个循环。一切都很顺利，直到我在障碍物上添加了第二个脚本，使它们垂直移动。添加脚本后，我收到错误："无法从源类型转换为目标类型"。

这是使对象循环（Cs）的脚本：

public class BgLooper : MonoBehaviour {
    int numBGPanels = 10;
    float cloudMax = 2.2f;
    float cloudMin = -0.2f;
    void Start() {
        GameObject[] clouds = GameObject.FindGameObjectsWithTag ("Cloud");
        foreach (GameObject cloud in clouds) {
            Vector3 pos = cloud.transform.position;
            pos.y = Random.Range(cloudMin, cloudMax);
            cloud.transform.position = pos;
        }
    }
    void OnTriggerEnter2D(Collider2D collider) {
        Debug.Log ("Triggered: " + collider.name);
        float widthOfBGobject = ((BoxCollider2D)collider).size.x;
        Vector3 pos = collider.transform.position;
        pos.x += widthOfBGobject * numBGPanels;
        if (collider.tag == "Cloud") {
            pos.y = Random.Range(cloudMin, cloudMax);
        }
        collider.transform.position = pos;
    }
}

这是让顽固分子移动的脚本（Js）：

var maxX = 6.1;
var minX = -6.1;
var maxY = 4.2;
var minY = -4.2;
var moveSpeed = 0.3;
private var tChange: float = 0; // force new direction in the first Update
private var randomX: float;
private var randomY: float;
function Update () {
    // change to random direction at random intervals
    if (Time.time >= tChange){
        randomX = Random.Range(-2.0,2.0); // with float parameters, a random float
        randomY = Random.Range(-2.0,2.0); //  between -2.0 and 2.0 is returned
        // set a random interval between 0.5 and 1.5
        tChange = Time.time + Random.Range(0.5,1.5);
    }
    transform.Translate(Vector3(randomX,randomY,0) * (moveSpeed / 15) * Time.deltaTime);
    // if object reached any border, revert the appropriate direction
    if (transform.position.x >= maxX || transform.position.x <= minX) {
        randomX = -randomX;
    }
    if (transform.position.y >= maxY || transform.position.y <= minY) {
        randomY = -randomY;
    }
    // make sure the position is inside the borders
    transform.position.x = Mathf.Clamp(transform.position.x, minX, maxX);
    transform.position.y = Mathf.Clamp(transform.position.y, minY, maxY);
}

void OnTriggerEnter2D(Collider2D collider) {
    Debug.Log ("Triggered: " + collider.name);
    //change this line
    float widthOfBGobject =  collider.bounds.size.x;
    Vector3 pos = collider.transform.position;
    pos.x += widthOfBGobject * numBGPanels;
    if (collider.tag == "Cloud") {
        pos.y = Random.Range(cloudMin, cloudMax);
    }
    collider.transform.position = pos;
}