Board invisible

[bobblkabb]

Why is that board invisible? There supposed to be one where the screws are.
Already looks opaque in preview mode.

preview
rendered

// Target-Connector
cube_cs = new_cs(origin=[20,5,0-verschiebung], axes=[[0,0,1],[0,1,0]]);
cube_cs2 = new_cs(origin=[breite-20,5,0-verschiebung], axes=[[0,0,1],[0,1,0]]);
// Screws
schraube_cs = ISO4017_conn("root","M4",20);
unterleg_cs = ISO7089_conn("top","M4");

// Position screws
align(schraube_cs,cube_cs) DIN912("M4");
align(unterleg_cs,cube_cs) ISO7089("M4");
align(schraube_cs,cube_cs2) DIN912("M4");
align(unterleg_cs,cube_cs2) ISO7089("M4");

// Show
show_cs(cube_cs);
show_cs(cube_cs2);

[berndhahnebach]

Would you give more informations? Is this openscad code?