PHP not able to read $_FILES - php

Question

I'm trying to read $_FILES uploaded by my AJAX upload form. This is the POST request:
POST myhost.net/csv.php
Host: myhost.net
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:36.0) Gecko/20100101 Firefox/36.0
Accept: application%2Fjson%2C%20text%2Fjavascript%2C%20*%2F*%3B%20q%3D0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
X-Requested-With: XMLHttpRequest
X-File-Name: Europe_1351.csv
Content-Type: multipart/form-data; charset=UTF-8
Pragma: no-cache
Cache-Control: no-cache
Referer: http://myhost.net
Content-Length: 26
Cookie: PHPSESSID=kourjvs7rm980d2cg4qvaav965
Connection: keep-alive
And on the server side, I got:
var_dump( $_FILES );
Even though 'multipart/form-data' is set, there aren't any data in $_FILES variable. Does this have something to do with PHP configuration? Thanks!
EDIT:
Here is my code:
<script src="//raw.githubusercontent.com/LPology/Simple-Ajax-Uploader/master/SimpleAjaxUploader.js">
$(document).ready(function()
{
var sizeBox = document.getElementById('sizeBox');
var uploader = new ss.SimpleUpload({
button: 'uploadButton', // file upload button
url: 'csv.php', // server side handler
name: 'uploadfile', // upload parameter name
contentType: 'multipart/form-data',
responseType: 'json',
allowedExtensions: ['csv'],
maxSize: 10 * 1024, // kilobytes
hoverClass: 'ui-state-hover',
focusClass: 'ui-state-focus',
disabledClass: 'ui-state-disabled',
onSubmit: function(filename, extension)
{
this.setFileSizeBox(sizeBox); // designate this element as file size container
},
onComplete: function(filename, response)
{
if (!response) {
alert(filename + 'upload failed');
return false;
}
alert( 'file ' + response.data + ' uploaded successfully ');
// do something with response...
}
});
});
</script>
<div id='uploadButton'>
CSV
</div>
<div id='sizeBox'>
size
</div>

Answer 1

Use php inbuilt function print_r();
print_r($_FILES);