WP_Query in external file (Ajax Call)

Via ajaxSubmit i’m submitting a form.
First i kept getting the message that WP_Query did not exist. After a lot of searching i found that i had to include the wp-blog-header file. Since i did that, i don’t get errors anymore.

However when i do:

$loop = new WP_Query(  array( 'post_type' => 'calculator')  );
while ( $loop->have_posts() ) : $loop->the_post();
 the_title();
endwhile;
?>

(or other things i’ve tried) It appears that there are no posts since nothing happens in my loop.

Would be awesome if somebody could help me out..
Thanks in advance.

Rick