-Shader Unsupported... no vertex shader- breaking graphics in HTML5 export

Hey CommUnity,

I’ve been putting together a puzzle game using portals that works fine in Unity web player and on mobile. Here’s a graphic of what the portals look like:

However, when I export to HTML5, I get a series of warnings:

WARNING: Shading Unsupported: ‘Standard’ - Pass ‘FORWARD’ has no vertex shader
WARNING: Shading Unsupported: ‘Standard’ - Pass ‘FORWARD_DELTA’ has no vertex shader
WARNING: Shading Unsupported: ‘Standard’ - Pass ‘SHADOWCASTER’ has no vertex shader
WARNING: Shading Unsupported: ‘Standard’ - Pass ‘DEFERRED’ has no vertex shader
WARNING: Shader Unsupported: ‘Standard’ - All passes removed
WARNING: Shader Unsupported: ‘Custom/FillZValue’ - Pass ‘’ has no vertex shader

The ‘FillZValue’ shader is used by the portals. When portals appear in game, they are completely black:

I would love any help in fixing this, as it is preventing me from releasing my game in html5. I will admit that I am a shader amateur, and the shader causing trouble was obtained from a 3rd party and I don’t fully understand it. If you help I’ll give you my first born or something.

Here is the text of the trouble shader:

Shader "Custom/JustZValue" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
	}
	SubShader {
		Tags { "RenderType"="Opaque" "Queue"="Background-10" }
		LOD 200
		
		ColorMask 0
		
		CGPROGRAM
		#pragma surface surf Lambert

		sampler2D _MainTex;
		
		struct Input {
			float2 uv_MainTex;
		};

		void surf (Input IN, inout SurfaceOutput o) {
			half4 c = tex2D (_MainTex, IN.uv_MainTex);
			o.Albedo = c.rgb;
			o.Alpha = c.a;
		}
		ENDCG
	} 
	FallBack "Diffuse"
}

Found the answer. The issue was actually in another custom shader, which contained the code “#pragma exclude_renderers gles flash”. WebGL uses gles, and that line stopped the shader for compiling for it.