jQuery Ajax call returns null in ASP.Net

My insert is inserting data very well but the issue is that after inserting there is jquery pop error message saying null, when i click on the ok button it shows anothere error. Meanwhile the data inserted very well into table.

 //insert Modal details
               $("#btnInsertR").on("click", function () {
                   if ($(this).val().toLowerCase() == 'save') {
                       $("#lblText").html('Record saved successfully.');
                   }
                   
                   $('#dialog').fadeIn('slow').delay(1000).fadeOut('slow');
               });
                   var id = $('.id').html().trim();
                   var fname = $('.fname').html().trim();
                   var senddate = $('.senddate').html().trim();
                   var username = $('.username').html().trim();
                   var fusername = $('.fusername').html().trim();
                   var scontent = $('.scontent').html().trim();
                   var spostDate = $('.spostDate').html().trim();
                   var simagename = $('.simagename').html().trim();
                   var spath = $('.spath').html().trim();
                   // If you ant to insert "PROFILEPHOTOS/Test.jpg" format then use the below line
                   var fimagename = $('.fimagename').attr('src').slice(($('.fimagename').attr('src').lastIndexOf('/') + 1), $('.fimagename').attr('src').length);
                   // var imagename1 = $('.imagename1').attr('src').slice(($('.imagename1').attr('src').lastIndexOf('/') + 1), $('.imagename1').attr('src').length);
                   //If you ant to insert "Test.jpg" format then use the below line

                   var comments = $("#cshare").val();
                   $.ajax({
                       type: "POST",
                       url: "Timeline.aspx/GetInsertReShare",
                       data: '{id:"' + id + '",fname:"' + fname + '",senddate:"' + senddate + '",username:"' + username + '",fusername:"' + fusername + '",scontent:"' + scontent + '",comments:"' + comments + '",spostDate:"' + spostDate + '",simagename:"' + simagename + '",spath:"' + spath + '",fimagename:"' + fimagename + '"}',
                       contentType: "application/json; charset=utf-8",
                       dataType: "json",
                       success: function (response) {
                           alert(response.d);
                           $('#myModalreshare2').modal('hide');

                           // clear value
                           $(".id").html('');
                           $(".fimagename").attr('src', '');
                           $(".senddate").html('');
                           $(".username").html('');
                           $(".fusername").html('');
                           $(".fname").html('');
                           $(".spostDate").html('');
                           $(".scontent").html('');
                           $(".simagename").html('');
                           $(".spath").html('');
                       },
                       failure: function (response) {
                           alert(response.d);
                       },
                       error: function (response) {
                           alert(response.d);
                       }
                   });

                   return false;
               });
         
</script>

-------------------------


public static string GetInsertR(int id, string fname, string fusername, string scontent, string spostDate, string comments, string fimagename, string simagename, string senddate, string spath)
    {
        string constr = ConfigurationManager.ConnectionStrings["DB"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            using (SqlCommand cmd = new SqlCommand("INSERT INTO [SHPOSTS](UserName,FUserName,fName,SContent,ID,SPostDate,Comments,FImageName,SImageName,TotalCount,SPath) VALUES(@UserName,@FUserName,@fName,@SContent,@ID,@SPostDate,@Comments,@FImageName,@SImageName,@TotalCount,@SPath)"))
            {
                cmd.Connection = con;
                cmd.CommandType = CommandType.Text;
               // cmd.Parameters.AddWithValue("@ID", id);

                cmd.Parameters.AddWithValue("@UserName", HttpContext.Current.Session["userName"].ToString());
                cmd.Parameters.AddWithValue("@FUserName", fusername);

                cmd.Parameters.AddWithValue("@fName", fname);
                cmd.Parameters.AddWithValue("@SContent", scontent);
                cmd.Parameters.AddWithValue("@SPostDate", spostDate);
                cmd.Parameters.AddWithValue("@ID", id);
                cmd.Parameters.AddWithValue("@Comments", comments);
                cmd.Parameters.AddWithValue("@FImageName", fimagename);
                cmd.Parameters.AddWithValue("@SImageName", simagename);
                cmd.Parameters.AddWithValue("@TotalCount", 1);
                cmd.Parameters.AddWithValue("@SPath", spath);
                con.Open();
                cmd.ExecuteNonQuery();
                con.Close();
            }
        }
        return "Submited";
    }