Request.Files is empty only in ie10 using xmlHttpRequst and ashx

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C#

ASP.NET

Javascript

HTML5

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I am using HTML5 Drag&Drop File Upload with c# asp.net . In all browsers everything work fine, but in IE10 I can't get the files in the server in order to save them. I've tried everything and nothing works. please help.

here is my code:

javascript & HTML:

function uploadFile(index) {
    var files = window.opener.files; //get the files from drag area which is in window.opener
    for (var i = index; i < (index + files.length); i++) {
       debugger;
       var size = fixSize(files.item(i - index).size);
       var name = files.item(i - index).name;
       xhr.push(new XMLHttpRequest()); //create new xhr and push it to xhr array
       //var form = window.opener.document.getElementById('ddform');
       //var data = new FormData(form);
       var data = new FormData();
       data.append("index", i);
       data.append("fileName", name);
       data.append("file", files.item(i - index));
       xhr[i].open('POST', "HandlerUploadFiles.ashx", true);
       xhr[i].send(data);
    }
}

c#, using IHttpHandler:

public class HandlerUploadFiles : IHttpHandler, IRequiresSessionState
{
    public void ProcessRequest(HttpContext context)
    {
       // context.Response.ContentType = "text/plain";
       string fileName = context.Request["fileName"];
       string postedFile = context.Request["file"]; // returns string : {"object file"}
       HttpFileCollection fileCollection = context.Request.Files; // always empty!!!
       ...
    }
}

The problem in IE:
The server side code hits at ProcessRequest function.
The error I get while debugging: the collection : context.request.Files is empty (count=0) .
However, the other strings values (like fullName) from XHR can be retrieved .
I thought maybe I don't send the file correctly, but in searches I did - this was the way to send it.
Like I mention before- in FF and Chrome the program works excellent

Thanks for any help.