Callback failing if contains ajax

I'm trying to add a callback to a pre existing function in the jquery plugin nitelite https://github.com/premasagar/nitelite - The callback works fine http://jsfiddle.net/HPc4e/2/ - unless I have ajax in the callback?

Appropriate section of close function:

// Blah blah ...

else {

    showFlash();

    this.overlay.remove();

    this.container
        .empty()
        .remove();

    $(this).triggerHandler('close');

    // Add callback
    if (typeof callback == "function") {
        callback();
    }

}
return this;

Callback:

lb.close(undefined, 'click', function() {
    $.ajax({
        type: 'POST',
        url: url,
        data: {submit: $(this).val()},
        dataType: 'json',
        success: function(data) {
            lightbox('Lightbox 2', '<p>Oh hi</p>', 'lightbox2');
        }
    });
});

Thanks

I suspect that your callback is throwing an exception.

What is the value of this supposed to be when it's invoked? Are you sure it's pointing at a jQuery compatible element that has a .val() method?