function loadLightbox () 
{
    $('#sharepointSonderheftLayer').click();
}

$(document).ready(function() {
    $("#sharepointSonderheftLayer").fancybox({
        'type': 'iframe',
        'width': 800,
        'height': 500,
        'autoDimensions': false,
        'transitionIn': 'fade',
        'transitionOut': 'fade'
    });

    loadLightbox();
});