File uploading with XMLHttpRequest Undefined index

Question

I've searched around and could not find the answer to my problem. I've tried tons of stuff and it didnt work.

Whenever I'm sending a file via XMLHttpRequest to my swfupload.php my swfupload.php doesnt see the $_FILES

Here is my HTML

<form id="FlashUpload">
    <div class="fUpload">
        <label for="fileToUpload">Select a swf to Upload</label><br />
        <input type="file" name="upfile" id="fileToUpload" onchange="fileSelected();" accept="application/x-shockwave-flash">
        <input type="button" value="Upload" id="buttonToUpload" onclick="uploadFlash();"/>
        <div id="fError"></div>
    </div>
    <div style=" display:none;" class="meter animate">
        <span style="width: 0%;"><span></span></span>
    </div>
</form>

and here is my javascript file

function uploadFlash() {
    var client = new XMLHttpRequest();
    var file = document.getElementById('fileToUpload');

    var formData = new FormData();
    formData.append("upfile", file.files[0]);


    client.open("post", "/swfupload.php", true);
    client.setRequestHeader("Content-Type", "multipart/form-data");
    client.send(file);  /* Send to server */ 

    client.onreadystatechange = function() 
    {
        if (client.readyState === 4 && client.status === 200) {
            var return_data = client.responseText;
            $("#fError").text(return_data);
        }
    }
}

This is the part where I get my error in PHP

if (!isset($_FILES['upfile']['error'])) {
    throw new RuntimeException($_FILES['upfile']['error']);
}

I'm not sure if it has anything to do with me being in WAMP

The error: