Known problems:
Depending on your version of Wordpress you may the following php error:
Warning: extract(): First argument should be an array in /home/yoursite/public_html/wp-includes/functions.php on line 2109
To fix:
open wp-includes/functions.php
goto to line number 2109
you will find something like
extract($wp_query->query_vars);
and change it to:
if (is_array($wp_query->query_vars)) extract($wp_query->query_vars);