Null Reference Exception on instantiated objects script.

I am instantiating an object over a Network using an RPC. The object instantiates fine but if I try accessing the script when it is instantiated I get a null reference exception on the client and server.

This is the RPC.

 // Instantiate a Arrow projectile across the network.
     [RPC]
     void SpawnProjectileArrow(Vector3 position, Quaternion rotation) {
 
         GameObject arrow = Instantiate(projectileArrowPrefab, position, rotation) as GameObject;
         arrowProjectileScript aScript = arrow.GetComponent<arrowProjectileScript>();
         
     }

The "arrowProjectileScript" is attached to the projectileArrowPrefab.

Any Ideas on what is causing this?

Thanks - Matt