Pixel Shader 'stage Did Not Run'

Pixel Shader 'stage Did Not Run'
Hi Guys,
 
I am scratching my head with this one.
 
I have a basic pixel shader that should just fill the geometry white
 

float4 main() : SV_TARGET
{
        return float4(1.0f, 1.0f, 1.0f, 1.0f);
}

And a vertex shader that leaves the geometry un transformed

float4 main(float4 pos : POSITION) : SV_POSITION
{
        return pos;
}

I can see in the debugger that the geometry is rendering ok, but the pixel shader seems to be bypassed.



I can see from the debugger that the shader has loaded correctly.

I am at a loss as to why this doesn't render anything on screen.

Any advice is greatly appreciated