When upgrade unity to 5.5.0f3, this shader can't work anymore

it works good when I use unity version 5.3.4. But when I upgrade unity to 5.5.0,it's can't work anymore. And also it can't work on iOS platform because of "metal" issue.

 Shader "Image Effects/Fog of War"
 {
     Properties
     {
         _MainTex ("Base (RGB)", 2D) = "white" {}
         _FogTex0 ("Fog 0", 2D) = "white" {}
         _FogTex1 ("Fog 1", 2D) = "white" {}
         _Unexplored ("Unexplored Color", Color) = (0.05, 0.05, 0.05, 0.05)
         _Explored ("Explored Color", Color) = (0.35, 0.35, 0.35, 0.35)
     }
     SubShader
     {
         Pass
         {
             ZTest Always
             Cull Off
             ZWrite Off
             Fog { Mode off }
                     
 CGPROGRAM
 #pragma vertex vert_img
 #pragma fragment frag vertex:vert
 #pragma fragmentoption ARB_precision_hint_fastest 
 #include "UnityCG.cginc"
 
 sampler2D _MainTex;
 sampler2D _FogTex0;
 sampler2D _FogTex1;
 sampler2D _CameraDepthTexture;
 
 uniform float4x4 _InverseMVP;
 uniform float4 _Params;
 uniform float4 _CamPos;
 uniform half4 _Unexplored;
 uniform half4 _Explored;
 
 struct Input
 {
     float4 position : POSITION;
     float2 uv : TEXCOORD0;
 };
 
 void vert (inout appdata_full v, out Input o)
 {
     o.position = mul(UNITY_MATRIX_MVP, v.vertex);
     o.uv = v.texcoord.xy;
 }
 
 float3 CamToWorld (in float2 uv, in float depth)
 {
     float4 pos = float4(uv.x, uv.y, depth, 1.0);
     pos.xyz = pos.xyz * 2.0 - 1.0;
     pos = mul(_InverseMVP, pos);
     return pos.xyz / pos.w;
 }
 
 fixed4 frag (Input i) : COLOR
 {
     half4 original = tex2D(_MainTex, i.uv);
 
 #if SHADER_API_D3D9
     float2 depthUV = i.uv;
     depthUV.y = lerp(depthUV.y, 1.0 - depthUV.y, _CamPos.w);
     float depth = UNITY_SAMPLE_DEPTH(tex2D(_CameraDepthTexture, depthUV));
     float3 pos = CamToWorld(depthUV, depth);
 #else
     float depth = UNITY_SAMPLE_DEPTH(tex2D(_CameraDepthTexture, i.uv));
     float3 pos = CamToWorld(i.uv, depth);
 #endif
     
     // Limit the fog of war to sea level
     if (pos.y < 0.0)
     {
         // This is a simplified version of the ray-plane intersection formula: t = -( N.O + d ) / ( N.D )
         float3 dir = normalize(pos - _CamPos.xyz);
         pos = _CamPos.xyz - dir * (_CamPos.y / dir.y);
     }
     
     float2 uv = pos.xz * _Params.z + _Params.xy;
     half4 fog = lerp(tex2D(_FogTex0, uv), tex2D(_FogTex1, uv), _Params.w);
     
     return lerp(lerp(original * _Unexplored, original * _Explored, fog.g), original, fog.r);
 }
 ENDCG
         }
     }
     Fallback off
 }