iPhone: Use of undeclared identifier '_patchFragColor'

A shader works in preview, but fails when launching. Below is the original shader. Following that is the error and generated shader by Unity.

Since this code is generated, is it possible to circumvent the problem?

 Shader "RH/EfficientDot" {
 Properties {
     _MainTex ("Main", 2D) = "white" {}
     _GridTex ("Grid", 2D) = "white" {}
 }

 SubShader {
     Pass{
         Blend SrcAlpha OneMinusSrcAlpha
         Lighting Off ZWrite Off 

         GLSLPROGRAM
         #ifdef VERTEX

         varying vec2 the_uv;
         varying vec4 color;

         void main()
         {
             color = gl_Color;
             gl_Position = gl_ModelViewProjectionMatrix * gl_Vertex;
             the_uv = gl_MultiTexCoord0.st;
         }
         #endif

         #ifdef FRAGMENT
         uniform sampler2D _MainTex;
         uniform sampler2D _GridTex;
         varying vec2 the_uv;
         varying vec4 color;

         void main()
         {
             if (texture2D(_MainTex, the_uv).a * color.a > texture2D(_GridTex, vec2(gl_FragCoord.x, gl_FragCoord.y)*.25).a){
                 gl_FragColor = color; 
             } else {
                 gl_FragColor = vec4(0.0, 0.0, 0.0, 0.0);    
             }
         }
         #endif
         ENDGLSL
     }
 }
 }

When compiling, Xcode spits out an error below.

 -------- GLSL info log: ERROR: 0:31: Use of undeclared identifier '_patchFragColor'


 GLES20: failed to compile fragment shader:
 #define IN_HIGHP highp
 #define IN_MEDIUMP mediump
 #define IN_LOWP lowp
 precision mediump float;
 uniform lowp vec4 _unity_FogColor;
 varying lowp float _unity_FogVar;


 #define SHADER_API_GLES 1
 #define tex2D texture2D
 #line 13

             
                         


    uniform sampler2D _MainTex;
    uniform sampler2D _GridTex;
    varying vec2 the_uv;
    varying vec4 color;

    void main()
    {
     if (texture2D(_MainTex, the_uv).a * color.a > texture2D(_GridTex, vec2(gl_FragCoord.x, gl_FragCoord.y)*.25).a){
      lowp vec4 _patchFragColor;
 _patchFragColor = color;  _patchFragColor.rgb = mix (_unity_FogColor.rgb, _patchFragColor.rgb, _unity_FogVar); gl_FragColor = _patchFragColor;
  
     } else {
      _patchFragColor = vec4(0.0, 0.0, 0.0, 0.0); 
     }
    }