Unet Network How to generate out dynamic synchronous bullets

I want to dynamic synchronous generated out of bullets,but,The client and the server are not synchronized,I want to know what should I do ,The last error is **

OnObjSpawn netId: 11 has invalid asset Id
UnityEngine.Networking.NetworkIdentity:UNetStaticUpdate()

** .

Your bullet must be added to “Registered Spawnable Prefabs” in the NetworkManager.