AQUA Water null problem

I bought the full version of aqua water yesterday and i'm watching the video that were recommended in it on how to set it up: https://www.youtube.com/watch?v=ntTkuod3O-4&t=123s how ever when i add water just like in the video at 2:56 i get a red null error:

ArgumentException: The Object you want to instantiate is null. UnityEngine.Object.CheckNullArgument (System.Object arg, System.String message) (at C:/buildslave/unity/build/Runtime/Export/UnityEngineObject.cs:239) UnityEngine.Object.Instantiate[GameObject] (UnityEngine.GameObject original) (at C:/buildslave/unity/build/Runtime/Export/UnityEngineObject.cs:200) AQUAS_QuickSetup.AddWater () (at Assets/Editor/AQUAS_QuickSetup.cs:118) AQUAS_QuickSetup.OnGUI () (at Assets/Editor/AQUAS_QuickSetup.cs:51) System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)

I have some screenshots of my game and script here: http://imgur.com/a/vllrI How do i fix this? Please help!

[1]: http://imgur.com/a/vllrI