Blend 2 Texture with alpha

I try to do a shader that blend 2 texture and have alpha channel.

Shader "Blend 2 Textures + Alpha" { 
	
Properties {
	_Color ("Color Tint (A = Opacity)", Color) = (1,1,1,1)
	_Blend ("Blend", Range (0,1)) = 0.0 
	_MainTexture1 ("Texture1", 2D) = "" 
	_MainTexture2 ("Texture2", 2D) = ""
	_Mask ("Culling Mask", 2D) = "white" {}
    _Cutoff ("Alpha cutoff", Range (0,1)) = 0.1
}

Category {
	Material {
		Ambient[_Color]
		Diffuse[_Color]
	}

	// iPhone 3GS and later
	SubShader {
	Tags {"Queue" = "Transparent"}
    ZWrite On
    Cull Off
    Blend SrcAlpha OneMinusSrcAlpha
    AlphaTest GEqual [_Cutoff]
	 
	
	Pass {
		Lighting On
		
		SetTexture[_MainTexture1]
		SetTexture[_MainTexture2] { 
			ConstantColor (0,0,0, [_Blend]) 
			Combine texture Lerp(constant) previous
		}
		SetTexture [_Mask] {combine texture * previous}
        SetTexture[_Color] {Combine previous * constant ConstantColor[_Color]}
        
        
	}}
}}

This shader is similar to this:

Shader "MaskedTexture"
{
   Properties
   {
      _Color ("Color Tint (A = Opacity)", Color) = (1,1,1,1)
      _MainTex ("Base (RGB)", 2D) = "white" {}
      _Mask ("Culling Mask", 2D) = "white" {}
      _Cutoff ("Alpha cutoff", Range (0,1)) = 0.1
   }
   SubShader
   {
      Tags {"Queue"="Transparent"}
      Lighting Off
      ZWrite Off
      Blend SrcAlpha OneMinusSrcAlpha
      AlphaTest GEqual [_Cutoff]
      Pass
      {
         SetTexture [_Mask] {combine texture}
         SetTexture [_MainTex] {combine texture, previous}
         SetTexture[_MainTex] {Combine previous * constant ConstantColor[_Color]}
      }
   }
}

Second shader work perfectly.
I have problem with alpha channel of the first shader. There is a black line along border. I don’t understand. Somebody can help me?

Hi, I’m no shader expert, and probably I’m resurrecting this post, but I think for you or whoever finds this post, a good idea would be first step: mix each of the textures with the alpha mask by separate, and then, blend them together. Could it be a good idea? Again, just trying to help with a possible very wrong light bulb moment!