[PHP] What is wrong??????

[phpu]

I have this script to login to site:


......................
  if ($_POST['email'] == "" || $_POST['password'] == "")
    {
    print 'Email or password cannot be blank !<br><a href="user_login.php">Back</a>';
    exit;
    }
    include ("connect_mysql.php");
    $crpass=md5($_POST['password']);
    $sql = "SELECT * FROM users WHERE email='".$_POST['email']."' AND 
password='".$crpass."'";
    $result= mysql_query($sql);
    if(mysql_num_rows($result) != 1)
    {
       print 'Name or password do not match!<br><a href="user_login.php">Back</a>';
    exit;
     }
     mysql_close($connect);
     session_start();
     $_SESSION['email']=$_POST['email'];
     $_SESSION['password']=$crpass;
     $_SESSION['key_login']= session_id();

................................................................
Every time i run this script i got this error:( my apache server is very well 
cofigured)
Warning: Cannot send session cookie - headers already sent by (output started at 
c:\apache\htdocs\proiect_gsm\login.php:11) in c:\apache\htdocs\proiect_gsm\login.php 
on line 81