Yup I really can't see why you are trying to include a file and then echo a value within the include statement. If you want to use another file to echo a value, you can do this:
THEN, within your page.php script, you can do this:
OR, do this:
echo "$_GET variable not set.";
Does this help at all? Test it out and see what you think.
$get = (isset($_GET['aid'])) ? $_GET['aid'] : "$_GET variable not set";