Shader error: too many "TEXCOORD"

Questions & Answers
1

I wrote a surface shader that’s an extension to the bumped diffuse shader (ads snow based on world normal).
that worked, then I made a variant with specular, but that doesn’t compile.
I get the error:

Shader error in ‘Custom/snowBumpedSpec’: Program ‘frag_surf’, input semantic attribute “TEXCOORD” has too big of a numeric index (8) at line 74
Keywords: DIRECTIONAL, LIGHTMAP_OFF, DIRLIGHTMAP_OFF, SHADOWS_SCREEN

So apparently I use to many texcoord, which doesn’t make much sense to me, as I don’t use more than in my (snow) bumped diffuse shader.

Also, I looked at the built in Reflective/Bumped Specular shader,
and it’s just as complex; the same amount of textures, the same amount of parameters, and even 1 more uv-set (1 use the float2 uv_MainTex for both the diffuse and normalmap)

So anyone that can help me ?

Edit:
the shader:

Properties 
    {
 _MainColor ("Color", Color) = (1,1,1,1)
 _MainTex ("Texture", 2D) = "white" {}
 _SpecColor ("Specular Color", Color) = (0.5,0.5,0.5,1)
 _Shininess ("Shininess", Range (0.01, 1)) = 0.078125
 _BumpMap ("Bumpmap", 2D) = "bump" {}
 _SnowTex ("Snow", 2D) = "white" {}
 _SnowAmount ("Snow Amount", Range(0.0,5.0)) = 1.0
    }
    
    SubShader 
    {
      Tags { "RenderType" = "Opaque" }
      
      CGPROGRAM
      #pragma surface surf BlinnPhong
      #pragma target 3.0
      
      struct Input 
      {
          float2 uv_MainTex;//:TEXCOORD0;
          //float2 uv_BumpMap;
          float3 worldPos;
          float3 worldNormal;
 INTERNAL_DATA
      };
      
      float4 _MainColor;
      sampler2D _MainTex;
 float _Shininess;
      sampler2D _BumpMap;
      sampler2D _SnowTex;
      float _SnowAmount;
      
 void surf (Input IN, inout SurfaceOutput o) 
 {
        float4 tex = tex2D (_MainTex, IN.uv_MainTex)*_MainColor;
        float4 snow = tex2D (_SnowTex, IN.worldPos.xz);
        o.Normal = UnpackNormal (tex2D (_BumpMap, IN.uv_MainTex));           

        float snowfactor = 1 - WorldNormalVector(IN, normalize(o.Normal)).y;
        snowfactor = snow.a - snowfactor;
       
        if (_SnowAmount>1)
            snowfactor *= _SnowAmount;
        else
            snowfactor += (_SnowAmount-1)*2;
        snowfactor = saturate(snowfactor);
        tex = snow*snowfactor + tex*(1-snowfactor);
        o.Albedo = tex.rgb;
        o.Specular = _Shininess;
        o.Gloss = tex.a;
        o.Alpha = tex.a;
 }
      ENDCG
    } 
    
    Fallback "snowSpecular"

Edit2: the compiled shader:

Shader "Custom/snowBumpedSpec" 
{
    Properties 
    {
 _MainColor ("Color", Color) = (1,1,1,1)
 _MainTex ("Texture", 2D) = "white" {}
 _SpecColor ("Specular Color", Color) = (0.5,0.5,0.5,1)
 _Shininess ("Shininess", Range (0.01, 1)) = 0.078125
 _BumpMap ("Bumpmap", 2D) = "bump" {}
 _SnowTex ("Snow", 2D) = "white" {}
 _SnowAmount ("Snow Amount", Range(0.0,5.0)) = 1.0
    }
    
    SubShader 
    {
      Tags { "RenderType" = "Opaque" }
      
      // surface shader with errors was here
Pass { }
/*/* surface debug info:
 needs world normal vector
 needs world space position
 stuff performed in tangent space
 passes tangent-to-world matrix to pixel shader
*/
/* surface debug info:
 needs world normal vector
 needs world space position
 stuff performed in tangent space
 passes tangent-to-world matrix to pixel shader
*/
/* surface debug info:
 stuff performed in tangent space
*/
/* surface debug info:
 needs world normal vector
 needs world space position
 stuff performed in tangent space
 passes tangent-to-world matrix to pixel shader
*/
*/
#LINE 65

    } 
    
    Fallback "snowSpecular"
  }
2
  1. enable #pragma debug in shader, this will add comments to compiled shader.
  2. open compiled shader and you’ll see all semantics that really used in shader - there will be shadows textures and so on
  3. disable unused checks and calculations and shader - this can free some texture coordinates you need
  4. if nothing helps, try to use one mapping (tiling/offset) for many textures, for example, use uv_MainTex in tex2D methods for _MainTex and _BumpMap - this will free 1 texcoord