DOn't know whats the problem! PHP

1

this is the code:

<?php
require_once "dbconfig.php"; 
$sql = mysql_query("SELECT * FROM users11 WHERE username='".addslashes($_POST['username'])."'") or die("username was in correct. MySQL said".mysql_error());
$result = mysql_fetch_array($sql);

if($result['password'] == sha1($_POST['password'])) {
    session_start();
    header("Cache-control: private");
    $_SESSION[”sessioname”] = $_POST[’username’];
    header("location: protected.php");
}else{
    echo "Incorrect login details please try again.";
}

?>

this is the output:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at E:\xampp\htdocs\login2\dbconfig.php:4) in E:\xampp\htdocs\login2\login.php on line 7

Warning: Cannot modify header information - headers already sent by (output started at E:\xampp\htdocs\login2\dbconfig.php:4) in E:\xampp\htdocs\login2\login.php on line 8

Warning: Cannot modify header information - headers already sent by (output started at E:\xampp\htdocs\login2\dbconfig.php:4) in E:\xampp\htdocs\login2\login.php on line **10

can’t figure it out what’s the problem… any idea guys?
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