Shortcode problem

My WP settings
– WordPress : 2.6.8
– Theme : Arthémia, with some change
– plugin : NextGenGallery
– FAI : servhome.org
– URL : https://cinazadaire.new.fr

I create with more difficulty 1 shortcode function to show some posts in a page.
The function work but the posts don’t show the ohters shortcode for nextgengallery ex: [nggallery id=6] or [youtube FDxSekVs8Uo]

this my function :

function ad_newsletter($atts, $content = null) {
        extract(shortcode_atts(array(
	                "nwposts" => '5'
	        ), $atts));
			$retour='';
			foreach(explode(",",$nwposts) as $post) {
	            $data=get_post($post);
				$retour.='<div class="ll"><div class="title"><a href="'. get_permalink($post) . '" rel="bookmark">'. $data->post_title .'</a></div>
				<div class="spoiler">'. $data->post_content .'</div></div>';
			}
			return $retour;
}
add_shortcode("newsletter", "ad_newsletter");

i put [newsletter nwposts=”id1,id2,id3,…”] in a page (ids are the posts list)
you can see the result here in the section “Cours multimédia 2”

The problem comes certainly from$data->post_content

Could you tell me if there is a solution and what is the solution??
Thanks by advance