Updating a shader from Unity 3.3

Hi, I have a shader from a Unity project that was built for Unity 3.3. I'm looking for advice from a shader pro who might know where this shader is going wrong in Unity 4.5.

 Shader "Fog Of War/Soft (Indie)" {
     Properties {
         _FadeTime ("Fade Time", float) = 1
         _WorldTime ("World Time", float) = 0
         _Color ("Fog Color", Color) = (1, 1, 1, 0.5)
     }
 
     SubShader {
         Tags { "Queue"="Overlay-1" "RenderType"="Transparent" }
         Cull Back 
         Lighting Off 
         Fog { Mode Off }
 
         Pass {
             ZWrite On
             ZTest Always
             ColorMask 0
             
             CGPROGRAM
             
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
 
             float4 vert (appdata_base v) : SV_POSITION
             {
                 return mul(UNITY_MATRIX_MVP, v.vertex);
             }
 
             half4 frag (float4 i) : COLOR
             {
                 return 0;
             }
 
             ENDCG
         }
 
         Pass {
             Blend DstColor Zero
             ZWrite Off
             ZTest Equal
 
             CGPROGRAM
 
             #pragma vertex vert
             #pragma fragment frag
             #include "UnityCG.cginc"
             
             float4 _Color;
             float _FadeTime;
             float _WorldTime;
 
             struct output {
                 float4 pos : SV_POSITION;
                 half4 col : COLOR;
             };
 
             output vert (appdata_base v)
             {
                 float t;
                 output o;
                 
                 t = clamp(1 - ((_WorldTime - v.texcoord.x) / _FadeTime), v.texcoord.y, 1);
 
                 o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
                 o.col = t + (t * _Color * abs(1 - t));
                 
                 return o;
             }
 
             half4 frag (output i) : COLOR
             {
                 return i.col;
             }
 
             ENDCG
         }
     }
 }