[SFML 2.0, C++] Failed to find variable "..." in shader

#include <SFML/Graphics.hpp>
#include <assert.h>

int main()
{
    sf::VideoMode vidmode;
    vidmode.width = 800;
    vidmode.height = 600;
    vidmode.bitsPerPixel = 32;
    assert( vidmode.isValid() );
   
    sf::RenderWindow win( vidmode, "Light test" );
   
    sf::Event event;
   
    sf::Texture backgroundImage, light, playerTexture;
    assert( backgroundImage.loadFromFile( "data/background.png" ) );
    assert( light.loadFromFile( "data/lightFin.png" ) );
    assert( playerTexture.loadFromFile( "data/player.png" ) );
   
    backgroundImage.setRepeated( true );
    sf::Sprite background( backgroundImage );
    background.setTextureRect( sf::IntRect( 0, 0, vidmode.width, vidmode.height ) );
    sf::Sprite player( playerTexture );
   
    sf::Shader lightshader;
    lightshader.loadFromFile( "data/lightshader.frag", sf::Shader::Type::Fragment );
   
    while( win.isOpen() )
    {
        while( win.pollEvent( event ) )
        {
            if( event.type == sf::Event::Closed ) win.close();
           
        }
        sf::Vector2i mousePos = sf::Mouse::getPosition( win );
        lightshader.setParameter( "lightpos", mousePos.x, mousePos.y );
        lightshader.setParameter( "lightColor", sf::Color::Yellow );
        lightshader.setParameter( "screenHeight", vidmode.height );
        lightshader.setParameter( "lightAttenuation", 1.0f, 1.0f, 1.0f );
        lightshader.setParameter( "radius", 1.0f );
        lightshader.setParameter( "texture", light );
        //lightshader.setParameter("pos", 100.0f, 100.0f);
        //lightshader.setParameter("color", sf::Color(255, 128, 0, 255));
       
        player.setPosition( mousePos.x, mousePos.y );
       
        win.clear();
        win.draw( background, & lightshader );
        //win.draw(player, &lightshader);
        win.display();
    }
}