can't render shader on iOS althoungh it works in osx and simulator

i have a custom shader that i apply to the camera so get a nightvision effect. There is something weird going on with unity3d. i have encountered the problem before but can't remember how to fix it. I am using unity3d 3.5.

I run my game targeting mac os x and the shader works just fine. When i target iOS and export a build i get a black screen (black screen because the shader is for the camera view, i can still see GUITextures). The thing is that the shader isn't using anything that iOS can't handle and due to my previous experiences (when i fixed the problem) i'm sure it's something in the settings of unity3d.

here is my shader:

 Shader "Custom/nightvisionShader" {
     Properties {
         _MainTex ("Texture ", 2D) = "white" {}
         _noiseTex ("noiseTex ", 2D) = "white" {}  
         _maskTex ("mask tex",2D) = "white" {} 
         _elapsedTime("elapsed time",Float) = 0 // seconds
         _luminanceThreshold("luminance threshold",Float) = .2 // 0.2
         _colorAmplification("color amplification",Float) = 4 // 4.0
         _effectCoverage("effect coverage",Float) = .5 // 0.5
     }
     SubShader {
         Tags { "RenderType"="Transparent" }
         //LOD 200
         
         CGPROGRAM
         #pragma surface surf Lambert
 
         sampler2D _MainTex;
         sampler2D _noiseTex;
         sampler2D _maskTex;
         float _elapsedTime;
         float _luminanceThreshold;
         float _colorAmplification;
         float _effectCoverage;
 
         struct Input {
             float2 uv_MainTex;
             float2 uv_noiseTex;
             float2 uv_maskTex;
             
         };
 
         void surf (Input IN, inout SurfaceOutput o)
          {
              half4 finalColor;         
             if (IN.uv_MainTex.x < _effectCoverage) 
                   {
                     float2 uv;  
                    
                     uv.x = 0.4*sin(_elapsedTime*50.0);                                 
                     uv.y = 0.4*cos(_elapsedTime*50.0);                                 
                     float m = tex2D(_maskTex, IN.uv_maskTex).r;
                     half3 n = tex2D(_noiseTex,(IN.uv_noiseTex*3.5) + uv).rgb;
                     half3 c = tex2D(_MainTex, IN.uv_MainTex + (n.xy*0.005)).rgb;
   
                     float lum = dot(float3(0.30, 0.59, 0.11), c);
                     if (lum < _luminanceThreshold)
                       c *= _colorAmplification; 
   
                     half3 visionColor = float3(0.1, 0.95, 0.2);
                     finalColor.rgb = (c + (n*0.2)) * visionColor * m;
                   o.Albedo = finalColor;
                     }
            else
                {
                 o.Albedo = tex2D(_MainTex, IN.uv_MainTex);
               //  o.Emission = half4(.5,.5,.5,1);
                }
             
         }
         ENDCG
     } 
     FallBack "Diffuse"
 }

and the code that renders the material to which the shader is attached:

 void OnRenderImage (RenderTexture source,  RenderTexture destination) 
     {    
         //overlayMaterial.SetTexture ("_MainTex", source);
         //overlayMaterial.SetTexture ("_noiseTex", Resources.Load("nightvision/noise_tex6") as Texture2D);
         //overlayMaterial.SetTexture ("_maskTex", Resources.Load("nightvision/binoculars_mask") as Texture2D);    
         overlayMaterial.SetFloat ("_elapsedTime", Time.time);    
         
         Graphics.Blit (source, destination, overlayMaterial, -1);
     }

Again, the code works well in simulator and os x(even in the web player).

What am i setting wrong?