[FlyingDutchman]

shouldn't userid <> $userid be replaced by: userid='$userid'?

try this code instead then:

PHP Code:

    if ($exists=$DB_site->query_first("SELECT userid FROM user WHERE username='".addslashes(htmlspecialchars($ausername))."' AND userid='$userid'")) {
        echo "There is already an ".makelinkcode('user',"user.php?do=edit&userid=$exists[userid]",1)." named <b>".htmlspecialchars($ausername)."</b>";
        exit;
    }