I know before sending their should not be any printing statement on the screen. and I haven't did that in my code. Their is no echo statement no print statement.
warning Cannot modify header information - headers already sent by (output started at /home/oxfordmo/public_html/php/user/header.php:18) in /home/oxfordmo/public_html/php/user/index.php on line 21
Its showing error in header file.
Indexfile line 21
header("location:user.php?f=".base64_encode($_SESSION['firstname'])."&l=".base64_encode($_SESSION['lastname']));
and header file 15-20
<div id="wrapperheader">
<div id="menu">
<ul>
<li class="active"><a href="">Company</a></li>
<li><a href="">Services</a></li>
<li><a href="">Gallery</a></li>