网站-php上传文件出现错误，求大家解释一下，怎么修改？

<code> <?phprequire ('config.php');?><meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>=SITE_NAME?></title>
<p><b><a href="<?=SITE_DIR?>">=SITE_NAME?></a><br></b>=SITE_ADV?></p>
<br><p></p>
<form enctype="multipart/form-data" action="upload.php" method="post">
<input type="file" name="uploadfile"><input type="submit" value="上传">
</form>       </code>

<code> <?phpdefine ('SITE_NAME','外链盘');define('SITE_ADV','文件保存5天，最大10MB。随时删除，请勿上传重要文件。全部公开，请勿上传私密文件。');define('SITE_DIR','http://www.abc.com/'); //包含尾部"/"define('UPLOAD_DIR','u/'); //包含尾部"/","u"目录及根目录设为777define('MAX_SIZE','99999999999999999999'); //文件最大字节大小$valid_suffix = array('.php','.asp','.aspx');//不允许上传类型function valid_suffix($suffix){    global $valid_suffix;    if (!in_array($suffix,$valid_suffix)){        return true;    }else{        return false;    }}?></code>

<code> <?phprequire ('config.php');if($_FILES['uploadfile']['error']>0){    $uploadtype = false;    switch($_FILES['uploadfile']['error']){    }}$suffix = strtolower(substr($_FILES['uploadfile']['name'],-4));    if(!valid_suffix($suffix)){    $uploadtype = false;}    if($uploadtype === false){}else{$userip = ip2long($_SERVER['REMOTE_ADDR']);$time = time();$newpath = UPLOAD_DIR . $time .'x'. $userip . $suffix;if(is_uploaded_file($_FILES['uploadfile']['tmp_name'])){if(!move_uploaded_file($_FILES['uploadfile']['tmp_name'],$newpath)){$uploadtype = false;}else{$uploadtype = true;}}else{$uploadtype = false;}}if($uploadtype === false){}else{setcookie('uploaded',$time.'x'.$userip.$suffix.'|'.$_COOKIE['uploaded'],time()+3600*24*365);}?><meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>=SITE_NAME?></title>
<p><b><a href="<?=SITE_DIR?>">=SITE_NAME?></a><br></b>=SITE_ADV?></p>
<br><?phpif ($uploadtype === false){?><p><b>上传失败！</b><br><br>文件不存在，过大或不允许该扩展名。<br><br><a href="<?=SITE_DIR?>">重新上传</a></p>
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<?php }else{?><p><b>上传成功！</b><br><br>文件代码：<br>标准：<input value="<?=SITE_DIR.$newpath?>" style="width:500px;" onclick="this.select();"><br>HTML：<input value="<a href=<?=SITE_DIR.$newpath?> target=_blank>点此查看文件[xxcv.net]</a>" style="width:500px;" onclick="this.select();"><br><br>图片代码：<br>论坛：<input value="[img]<?=SITE_DIR.$newpath?>[/img]" style="width:500px;" onclick="this.select();"><br>HTML：<input value="<img src=<?=SITE_DIR.$newpath?>>" style="width:500px;" onclick="this.select();"><br><br><a href="<?=SITE_DIR?>">继续上传</a></p>
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<?php }?></code>

<code>  <meta http-equiv="refresh" content="0;></code>

最后一个文件夹U，出现这样的错误