Every now and then I run into the problem where pagination doesn’t work in a custom page template. The problem usually lies in my handling of query_posts.

The solution is to write the query as follows:

<?php
$paged = (get_query_var('paged')) ? get_query_var('paged') : 1;
$args = array(
  'author' => 4,
  'paged' => $paged
);
 
query_posts($args); 
?>

[source]

Enjoy!