List pages in two columns

Hi,

I’m using the code below to display a list of pages in two column, with specific meta key.
Works fine but when I repeat the code to display second set of pages with different meta key (custom field) it includes pages from first loop as well.
I need to run several sets of page lists with different meta keys.
How can I fix this?

Thanks.

Here is the code:

<?php
$page_s = explode("</li>",wp_list_pages('title_li=&meta_key=series&meta_value=three&echo=0&depth=1&style=none'));
$page_n = count($page_s) - 1;
$page_col = round($page_n / 2);
for ($i=0;$i<$page_n;$i++){
 if ($i<$page_col){
  $page_left = $page_left.''.$page_s[$i]."</li>";
 }
 elseif ($i>=$page_col){
  $page_right = $page_right.''.$page_s[$i]."</li>";
 }
}
?>
<center>
<h3>3 Series</h3>
<ul id="twocol_list_left">
<?php echo $page_left; ?>
</ul>
<ul id="twocol_list_right">
<?php echo $page_right; ?>
</ul>

</center>