管理员用户登陆不了,,老是跳到另到后台又马上跳回到登陆框,,是怎么回事啊

管理员用户登陆不了,,老是跳到另到后台又马上跳回到登陆框,,是怎么回事啊

发代码出来看看啦

<?php
require("include/is_login.php");
$user_type = is_login();
if ($user_type != "guest") {
if($user_type == "common_user") {
  echo '<meta http-equiv="refresh" c>';
} else if ($user_type == "enterprise") {
  echo '<meta http-equiv="refresh" c>';
} else if ($user_type == "admin") {
  echo '<meta http-equiv="refresh" c>';
}
} else if (isset($_POST["register"])) {
require("community_register_window.php");
} else {
if(($_POST["username"] != "") && ($_POST["password"] != "")) {
    require("include/login.php");
$user_type = login($_POST["username"], $_POST["password"]);
  if ($user_type == "guest") {
   $error_info = "<font color=red>非常抱歉, 登陆失败! <br>原因: 错误的用户名或密码.</font>";
   require("community_login_window.php");
  } elseif ($user_type == "common_user") {
  echo '<meta http-equiv="refresh" c>';
  } elseif ($user_type == "enterprise") {
  echo '<meta http-equiv="refresh" c>';
  } elseif ($user_type == "admin") {
  echo $_SESSION["username"];
  echo '<meta http-equiv="refresh" c>';
  } else {
  require("community_login_window.php");
  }
} else {
  require("community_login_window.php");
}
}
?>