Prefab creation

Unity Engine
1

Little help with an error

Transform nadePrefab;
GameObject nade = (GameObject)Instantiate(nadePrefab, transform.position, Quaternion.identity);
nade.rigidbody.AddForce(transform.forward * speed);

throws error

InvalidCastException: Cannot cast from source type to destination type.

2

Instantiate returns the same type you pass it, in you case a transform.

So:

Transform nade = (Transform)Instantiate(nadePrefab, transform.position, Quaternion.identity);