File upload File Size Error not displaying in Asp.net

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C#

.NET

.NET4

ASP.NET4

hi all
i have a file upload in my webform and i allow the maximum file size to be uploaded in my application is 2MB, Configuration is done in web.config file.But on the file upload if file size is greater than 1MB and less than 2mb then in this condition i displayed alert box that file size exceeds than 1MB.
It is working fine on localhost but when i deployed it on live server this is not working
Code is here

if (filFile.HasFile)
            {
                if (string.IsNullOrEmpty(script))
                {
                    //Uploaded file is valid, now we can do whatever we like to do, copying it file system,
                    //saving it in db etc.
                    try
                    {

                        if (filFile.HasFile)
                        {

                            int fileSize = filFile.PostedFile.ContentLength;
                            // if (fileSize > 1100000)
                            if (fileSize > 1024 * 1024)
                            {

                                Response.Write("<script> alert ('File size exceeds form 1MB.') </script>");
                                //Session["uploader_Else"] = "Else";
                                script = string.Format(SCRIPT_TEMPLATE, "File upload FAILED.", "false");
                                ClientScript.RegisterStartupScript(this.GetType(), "uploadNotify", script);

                            }
                            else
                            {
}

Kindly give me the reason why it is not working on live server although it is working fine on localhost.