PHP Version 5.2.2
im using full paths in all instances

ive chopped out the full path in my example
/home/cwcom/domains/xxxxx.co.uk/public_html/forums
include ('/home/xxxxx/domains/xxxxxxxx.co.uk/public_html/forums/includes/user_auth.inc.php');
the 2 paths in the /includes folder are also correct.
require_once( "/home/xxxxx/domains/xxxxxxx.co.uk/public_html/forums/includes/config.inc.php" );
require_once( "/home/xxxxx/domains/xxxxxx.co.uk/public_html/forums/libs/mysql.inc.php" );