Extremely simple dx11 shader compiles but fails to load with "Parameter incorrect"

Windows Phone
1

Sorry if this sounds stupid but even if i managed to create countless effects in monogame i’m getting a strange exception here and i dunnow where the issue is:
this is the full code of an extremely simple shader… that compiles fine but fails to load :frowning:

sampler2D mysampler;

float4 pscomplete(in float2 vertices : TEXCOORD0) : COLOR0    
{
    float4 colors;

    colors = tex2D(mysampler,vertices);

    return colors;
}
technique tech_complete    
{ 
    pass P0 { PixelShader = compile ps_4_0 pscomplete(); }
}