InvalidCastException in C#

I am trying to convert this Javascript to C#:

var bulletPrefab : Transform;

function Update().....

var bullet = Instantiate(bulletPrefab, GameObject.Find("gunPoint").transform.position, Quanternion.identity);
bullet.rigidbody.AddForce(transform.forward);

C#

public Transform bulletPrefab;

void Update () {
.....  

 GameObject bullet = (GameObject)Instantiate(bulletPrefab, GameObject.Find        ("gunPoint").tranform.position, Quanterion.identity);

bullet.rigidbody.AddForce(transform.forward * 2000);

When I play the game, I am getting this error "InvalidCastException: Cannot cast from source type to destination type." What am I doing wrong?

Have you tried replacing

GameObject bullet = (GameObject)Instantiate(bulletPrefab, 
    GameObject.Find("gunPoint").transform.position, Quanterion.identity);

with

Transform bullet = (Transform)Instantiate(bulletPrefab, 
    GameObject.Find("gunPoint").transform.position, Quanterion.identity);

?

If you need to get bullet as game object, you could do something like this:

Transform bulletTrans = (Transform)Instantiate(bulletPrefab, 
    GameObject.Find("gunPoint").transform.position, Quanterion.identity);
GameObject bullet = bulletTrans.gameObject;