fileupload control in web method

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File-Upload

how to get reference of fileupload control in static webmethod asp.net
please help me out

my aspx page

<asp:FileUpload ID="fileuploadreceipt" runat="server" />

and code behind

[WebMethod(EnableSession = true)]
    [ScriptMethod(ResponseFormat = ResponseFormat.Json)]
    public static string insertrow(string CMEX_ID, string CMED_ID, string CMET_TYPE_DESC, string CMED_EXP_DT, Int32 CMED_EXP_TYPE, string CMED_EXP_DESC, string CMED_EXP_QTY, string CMED_EXP_RATE, string CMED_EXP_AMT, string CMED_EXP_RCPT_FILE_NAME, string CMED_EXP_COMMENTS, string CMED_EXP_COMP_PAID,string CMED_UPD_USER)
    {

        string physicalpath = string.Empty;
        if (CMED_EXP_RCPT_FILE_NAME != null)
        {
            HttpPostedFile fileup = HttpContext.Current.Request.Files["fileuploadreceipt"];
            string Ext = Path.GetExtension(Convert.ToString(CMED_EXP_RCPT_FILE_NAME));
            string filename = Path.GetFileName(Convert.ToString(CMED_EXP_RCPT_FILE_NAME));
            physicalpath = filename.Replace(filename, "") + Guid.NewGuid().ToString() + Ext;
            fileup.SaveAs(HttpContext.Current.Server.MapPath(physicalpath + "~/Receipts/"));
        }

but i am getting httppostedfile null please help me out.