How to solved Authantication failed error when call webmethod?

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ASP.NET

When i am call webmethod and Redirect Page then getting Authentication failed error in browser console.

here is that code:

[WebMethod]
    public static void fileDownloadUsingWebMethod(object dataPath)
    {

            string saveBasePath = "";
            string folderName = "";

            saveBasePath = HttpContext.Current.Server.MapPath("~/developeruploads/MindShare/");
            folderName = "Mindshare";

            //[original name,renamed name]
            string[] strFileName = new string[2];
            strFileName = Convert.ToString(dataPath).Split(';');

            string strFilePath = Path.Combine(saveBasePath, strFileName[1]);

            FileInfo fi = new FileInfo(strFilePath);
            if (fi.Exists)
            {
                HttpContext.Current.Session["DwFolderName"] = folderName;
                HttpContext.Current.Response.Redirect("~/brightableweb/downloading.aspx?file=" + fi.Name.Replace("&", "_") + "&fileName=" + strFileName[0],false);

            }

    }