Can't move the prefab by Rigidbody2D component

Using Unity 5.0 .I write these codes to move my prefab:

    GameObject policeCarInstance = Instantiate(policeCar,enemySpawner.position, Quaternion.identity) as GameObject;
    Rigidbody2D policeCarRigidbody = policeCarInstance.GetComponent<Rigidbody2D>();
    policeCarRigidbody.velocity = new Vector2 (0f, -10f);

When the animator component of the prefab is disabled, the prefab moves correctly but when it’s enabled, the prefab doesn’t move.
The animation is simply 5 sprites of the different states of the police car’s lights.
Here’s a pic of the animator of the prefab:

42692-001.png

This code with exactly same properties and states works properly on Unity 4.6 (even when the animator component is enabled) but in Unity 5 it doesn’t work!

Is there any changes in Unity 5 that influence in the Rigidbody2D component?

Try this:

GameObject policeCarInstance = Instantiate(policeCar,enemySpawner.position, Quaternion.identity) as GameObject;
policeCarInstance.rigidbody2D.velocity = new Vector2 (0f, -10f);

If policeCar has a rigidbody2d, you can access it directly.