What value to pass in ajaxFileUpload plugin?

What value to pass in ajaxFileUpload plugin?

I am using this plugin for my file upload:
http://www.phpletter.com/our-projects/ajaxfileupload/
and it says there that :
fileElementId: the file type of input element id and it will be the index
of $_FILES Array()
You have to pass the id of the element.
I have several input type file elements and their ids are unique, i do
this to get their ids:
var input_files = [];
$('.file_upload').each(function () {
if ($(this).val()) {
input_files.push($(this).attr('id'));
}
});
And shift the ids one by one to pass it to the ajaxFileUpload. But i get
an error saying:
Malformed multipart POST: data truncated
Can someone point me to what ive done wrong?