咋老是出错呀？为什么实现不了刷新

<ul>
<li class="t3"></li>
<li class="t1">用户名：</li><li class="t2"><input name="User" type="text" class="text_1" id="User" size="30">
  <input name="pod" type="hidden" id="pod" value="0">
</li>
<li id="re_1" class="t3"></li>
<li class="t1">密 码：</li><li class="t2"><input name="Passwd" type="password" class="text_1" id="Passwd" size="30">
</li>
<li id="re_2" class="t3"></li>
<li class="t3">
  <input name="Submit3" type="button" class="button_1" value="确认登录" onClick="login();"> <input name="Submit3" type="button" class="button_1" value="免费注册">
</li>
<li class="t3"></li>
</ul>
<?php
session_start();
header('Content-type: text/html; charset=gb2312');
header ("Cache-Control: no-cache, must-revalidate");
header ("Pragma: no-cache");
unset($_SESSION['USERID']);
unset($_SESSION['USER']);
unset($_SESSION['TIME']);
unset($_SESSION['ATTE']);
?>// require_once("../Include/config.inc.php");
if($_GET["User"] !=""){
    $get_User = $_GET["User"];
}
else{
    echo "document.getElementById(\"re_1\").innerHTML = \"<font color=\\"#FF0000\\">用户名不能为空！</font>\";";
    echo "document.getElementById(\"User\").focus();";
    echo "document.getElementById(\"User\").select();";
    exit;
}
if($_GET["Passwd"] != ""){
    $get_Passwd = $_GET["Passwd"];
}
else{
    echo "document.getElementById(\"re_2\").innerHTML = \"<font color=\\"#FF0000\\">密码不能为空！</font>\";";
    echo "document.getElementById(\"Passwd\").focus();";
    echo "document.getElementById(\"Passwd\").select();";
    exit;
}