Simple editor question

hi.everyone.

I have a question about kirupa xml tuts:
http://www.kirupa.com/web/xml/examples/simpleeditor.htm

The simpleeditor doesn’t work fine on my site.
http://webstudio.com.cn/seditor/simple_editor.html

I think the simple_save.php is not work.

http://webstudio.com.cn/seditor/simple_save.php

 <?php 
$filename = "simple_edit.xml"; 
$raw_xml = file_get_contents("php://input"); 
  
print $raw_xml; 
  
$fp = fopen($filename, "w"); 
fwrite($fp, $raw_xml); 
fclose($fp); 
?> 

my phpinfo:

http://webstudio.com.cn/seditor/phpinfo.php

If my php version is low. how can I rewrite simple_save.php?

Please help me .I needed it.

Thanks a lot.