can_comment on facebook api always false

can_comment on facebook api always false

I am trying to get a comment info by a php script and i want to get if i
can reoly on comment or not by can_comment:
$comments_args = array('fields' =>
'can_comment,comments,created_time,from,message,user_likes,like_count',
'filter' => 'toplevel', 'summary' => 'true' , 'limit' => 200,
'access_token' => $token_access);
$facebook->api("/{$post_id}_{$comment_id}", "GET", $comments_args);
it gives: Array ( [can_comment] => [created_time] =>
2013-09-09T11:23:19+0000 [from] => Array ( [name] => sara [id] => 78687987
)
[message] => .....
[user_likes] =>
[like_count] => 156
[id] => .....
[comments] => Array
............
Can_comment is emtpty