Validate dynamically added FileUpload controls using JavaScript

I have used CustomeValidation for this.

HTML

<form id="form1" runat="server" enctype="multipart/form-data" method="post">
<span style="font-family: Arial">Click to add files</span>&nbsp;&nbsp;
<br />
<br />
<div id="FileUploadContainer">
    <!--FileUpload Controls will be added here -->
</div>
<div>
    <input id="file0" name="file0" type="file" onchange="ChangeBorder(this)" />
    <input id="Button1" type="button" value="add" onclick="AddFileUpload()" />
</div>
<br />
<asp:Button ID="btnUpload" runat="server" Text="Upload" OnClientClick="return ValidateFileUpload();"
    OnClick="btnUpload_Click" ValidationGroup="FileUpload" />
</form>

JavaScript

<script type="text/javascript">
    var counter = 1;
    //Adding File Upload Control
    function AddFileUpload() {
        var div = document.createElement('DIV');
        div.innerHTML = '<input id="file' + counter + '" name = "file' + counter +
        '" type="file" onchange="ChangeBorder(this)" />' +
        '<input id="Button' + counter + '" type="button" ' +
        'value="Remove" onclick = "RemoveFileUpload(this)" />';
        document.getElementById("FileUploadContainer").appendChild(div);
        counter++;
    }
    //Removing File Upload Control
    function RemoveFileUpload(div) {
        document.getElementById("FileUploadContainer").removeChild(div.parentNode);
    }

    //Validating File Upload Control
    function ValidateFileUpload() {
        var isValid = true;
        var fileUpload = document.getElementById("FileUploadContainer").getElementsByTagName("input");

        if (document.getElementById("file0").value == "") {
            isValid = false;
            document.getElementById("file0").style.border = "1px solid #DB2D2D";

        }

        for (var i = 0; i < fileUpload.length; i++) {
            if (fileUpload[i].type == "file") {
                if (fileUpload[i].value == "") {
                    isValid = false;
                    fileUpload[i].style.border = "1px solid #DB2D2D";
                }
            }
        }

        return isValid;
    }
    //Removing Border once the File Is Selected
    function ChangeBorder(fileupload) {
        fileupload.style.border = "";
    }
</script>

C#

protected void btnUpload_Click(object sender, EventArgs e)
{
    for (int i = 0; i < Request.Files.Count; i++)
    {
        HttpPostedFile PostedFile = Request.Files[i];
        if (PostedFile.ContentLength > 0)
        {
            string FileName = System.IO.Path.GetFileName(PostedFile.FileName);
            PostedFile.SaveAs(Server.MapPath("Files\\") + FileName);
        }
    }
}

Screenshot