'category__not_in' Parameter

Hello all.

I’m trying to exclude a category from some places. This one did what I wanted it to:

<?php query_posts(array(‘category__not_in’ => array(13))); ?>

This one isn’t working:

query_posts($query_string . “&orderby=comment_count&posts_per_page=25&(‘category__not_in’ => array(13)))”);?>

Neither is this one:

$args = array(
‘author’ => $curauth->ID,
‘order’ => DESC,
‘posts_per_page’ => 10
‘category__not_in’ => 13,
);
query_posts($args);?>

Any ideas? Thank you!