Surface lighting model standard not found

I want to make a shader for a balloon that uses the standard lighting model but with opacity tied to the Fresnel. This seemed straightforward enough, but when I make a shader using the Standard lighting model, I get an error stating "Surface lighting model standard not found."

I'm using Unity 5. I'm using the Standard shader on various objects and it is working fine. I'm starting with code copied off the internet for customizing the Standard lighitng model. That code is posted below.

Very confused about what I am doing wrong. The Lambert and BlinnPhong lighting models work fine, for what that's worth. I am also using Deferred rendering and DirectX 11 on a Windows 10 desktop.

 Shader "Custom/NewShader" 
 {
     Properties{
         _Color("Color", Color) = (1,1,1,1)
         _MainTex("Albedo (RGB)", 2D) = "white" {}
         _Glossiness("Smoothness", Range(0,1)) = 0.5
         _Metallic("Metallic", Range(0,1)) = 0.0
     }
         SubShader{
         Tags{ "RenderType" = "Opaque" }
         LOD 200
 
         CGPROGRAM
         #pragma surface surf Standard
         #pragma target 3.0
 
         sampler2D _MainTex;
 
     struct Input 
     {
         float2 uv_MainTex;
     };
 
     half _Glossiness;
     half _Metallic;
     fixed4 _Color;
 
     void surf(Input IN, inout SurfaceOutputStandard o) {
         fixed4 c = tex2D(_MainTex, IN.uv_MainTex) * _Color;
         o.Albedo = c.rgb;
         o.Metallic = _Metallic;
         o.Smoothness = _Glossiness;
         o.Alpha = c.a;
     }
     ENDCG
     }
 }