请教登陆验证为什么不行？sessoion问题

[itmylove]

login_ok.php是登陆验证处理程序：
<?php require("config.php");
if($textfield!=$key_id&&$textfield2!=$key_ps)
{
echo "用户错误,请返回重新输入";
}
else if($textfield==""&&$textfield2=="")
{
echo "用户错误,请返回重新输入";
}
else{

session_save_path(".");session_start();
session_register($key_id);
}
?>
config.php是配置文件
：
<?PHP
$local_name="localhost";
$key_db="guest";
$key_id="12344321";
$key_ps="12344321";
$mylink=mysql_connect($local_name,$key_id,$key_ps);
mysql_select_db($key_db,$mylink);

session_start();
session_register($key_id);
?>

出错:
Warning: Cannot send session cookie - headers already sent by (output started at e:\myweb\me_q\index.php:2) in e:\myweb\me_q\config.php on line 28

Warning: Cannot send session cache limiter - headers already sent (output started at e:\myweb\me_q\index.php:2) in e:\myweb\me_q\config.php on line 28

怎办啊?