Get response on OnComplete function of jQuery FileUpload plugin in ASP.Net

How to get response in else part of oncomplete function jquery file upload

alert(responseJSON.imsg); 

this is giving undefined error

        function UploadFeasibilty() {
            var uploader = new qq.FileUploader({
                element: document.getElementById("divFeasibiltyRep"),
                action: '../Applicant/FileUploadhandler.ashx?flnm=FeasibiltyReport',
                allowedExtensions: ['jpg', 'jpeg', 'pdf'],
                sizeLimit: 1024000,
                template: '<div class="qq-uploader">' +
            '<div class="qq-upload-drop-area"><span>Drop files here to upload</span></div>' +
            '<div class="qq-upload-button" width="100px">Upload Feasibility Report</div>' +
            '<div class="qq-upload-list"></div>' +
            '</div>',

                onComplete: function (id, fileName, responseJSON) {
                    debugger;
                    if (responseJSON.success == true) {
                        $("#<%= successmsgFeasibiltyRep.ClientID %>").text("Uploaded Successfully!");
                        $("#<%= hdnFeasibiltyReppath.ClientID%>").val(responseJSON.path);
                        $("#<%= hplFeasibiltyRep.ClientID%>").text("View File");
                        $("#<%= hplFeasibiltyRep.ClientID%>").attr("href", responseJSON.path.replace("~/", "../"));
                    }
                    else {
                        console.log(responseJSON);
                        alert(responseJSON.imsg);
                    }
                },
                error: function (e) {
                    console.log(e);
                },
                debug: true
            });
        }

                if (count > 1)
                {                
                    context.Response.Write("{success:false, imsg:\"Double extension are not allowed in File-Name, please rename and try again.\"}");
                }
                if (indexOf != -1)
                {                   
                    context.Response.Write("{success:false, imsg:\"Special character are not allowed in File-Name, please rename and try again.\"}");
                }