how to get response in OnClientUploadCompleteAll function in ajaxToolkit:AjaxFileUpload

hello to all

i use ajaxToolkit:AjaxFileUpload and i want in OnClientUploadCompleteAll function get response from server

for example pass e message and show it 

my code is

<ajaxToolkit:AjaxFileUpload ID="AjaxFileUpload2" AllowedFileTypes="jpg,jpeg,png" OnClientUploadCompleteAll="loadFuction" CssClass="FileAttachmentUpload" OnUploadComplete="anyUploader_UploadComplete" runat="server" />

            function loadFunction(e) {
                error = '<%=_errorMessage%>';
                console.log(error);
                if ($("#" + '<%=uploadStatus.ClientID%>').val() == "false") {
                    loadSliderPic();
                    changeText();
                }
                else {$("#AjaxFileUploader_FileStatusContainer").text('');$("#AjaxFileUploader_QueueContainer").text("خطا: ابعاد تصویر آپلود شده صحیح نمی باشد.").css("color", "red");

                }
            }

 public sting  _errorMessage = "error";

                        AjaxFileUploader.SaveAs(Server.MapPath("~/Uploades/SliderImg/" + e.FileName));
                        System.Drawing.Image objImage = System.Drawing.Image.FromFile(Server.MapPath("~/Uploades/SliderImg/" + e.FileName));
                        if (objImage.Width == 1003 && objImage.Height == 352)
                        {
                            System.IO.DirectoryInfo _imageAddress = new System.IO.DirectoryInfo(MapPath("~\\Uploades\\SliderImg"));
                            db.deleteXmlNode("SliderImageAddress", null);
                            int counter = 0;
                            foreach (System.IO.FileInfo item in _imageAddress.GetFiles())
                            {
                                if (item.Extension == ".jpg" || item.Extension == ".png" || item.Extension == ".jpeg")
                                {
                                    db.insertXmlNode("SliderInformation", "SliderImageAddress", "..\\Uploades\\SliderImg\\" + item.Name + ",", "Name", counter++.ToString());
                                }
                            }
                            uploadStatus.Value = "false";
                            _errorMessage = "Error in file size";

in console i see "error" Instead of "Error in file size"