This FS:

#version 400 core

#define FRAG_COLOR		0

precision highp float;
precision highp int;
layout(std140, column_major) uniform;

uniform sampler2D Diffuse;

in vert
{
	vec2 Texcoord;
	//sample vec2 Texcoord;
} Vert;

layout(location = FRAG_COLOR, index = 0) out vec4 Color;

void main()
{
	Color = texture(Diffuse, interpolateAtSample(Vert.Texcoord, gl_SampleID));
	//Color = texture(Diffuse, Vert.Texcoord);
}


fires

Shader status invalid: 0(21) : error C5229: Argument 1 for interpolateAtSample must have no component selection


This does not happen on C#
Commented lines is a temporary trick to get it working in the meanwhile