wp_insert_post fails with no error

I’m using ajax to pass a form’s variables to a php processing file from within a fancybox div.

Everything works, no errors, except the post never makes it to the database.

I have a form which is populated within a fancybox div:

<form id ="promo" name="promo" onsubmit="return submitForm();">
......form fields
</form>

I have an ajax function in header.php which calls the php script:

function submitForm() {
    $.ajax({type:'POST', url: '/wp-content/themes/buildcom/submit-form.php', data:$('#promo').serialize(), success: function(response) {
        $('#promo').find('.form_result').html(response);
    }});
    return false;
}

Finally I have the submit-form.php file which should insert the post, and returns true, but never creates a post no matter the parameters (post, page or custom post type):

$my_post = array(
  'post_title'    => 'tesssssssssssst',
  'post_content'  => 'test',
  'excerpt'       => 'excerpt',
  'post_status'   => 'publish',
  'post_type'     => 'post'
);
echo '<script>console.log("'.var_dump($my_post).'")</script>';

// Insert the post into the database
wp_insert_post($my_post, $wp_error);
$wp_error = wp_insert_post( $my_post, true);
                              echo '<pre>';
                              print_r ($wp_error);
                              echo '</pre>';

I get no error, it returns a post id, and if I dump the $my_post variable it returns all the fields without problem:

array(5) { ["post_title"]=> string(15) "tesssssssssssst" ["post_content"]=> string(4) "test" ["excerpt"]=> string(7) "excerpt" ["post_status"]=> string(7) "publish" ["post_type"]=> string(4) "post" }
94
its set

I’m stumped… someone please tell me what I’m missing.