this is because of the blank line between the php tags that you have added.
your code should not have any blank lines or spaces after the closing php tags:
<?php
ini_set('memory_limit', '256M');
ini_set('upload_max_filesize', '10M');
ini_set('post_max_size', '10M');
?><?php
# FileName="Connection_php_mysql.htm"
# Type="MYSQL"
# HTTP="true"
$hostname_powergallery = "[dbhost]";
$database_powergallery = "[dbname]";
$username_powergallery = "[username]";
$password_powergallery = "[password]";
$powergallery = mysql_pconnect($hostname_powergallery, $username_powergallery, $password_powergallery) or trigger_error(mysql_error(),E_USER_ERROR);
?>