Error generation plupload

I am trying to solve a problem with plupload, where I show an error in the upload window generated by upload.php. No matter what I do, I cannot create an error icon in the window. Although the warnings work fine, the file is always marked as successful. Can someone please tell me what I'm doing wrong here?

Error of my upload.php die('{"jsonrpc" : "2.0", "error" : {"code": 500, "message": "File upload failed."}, "id" : "id"}');

And this is javascript:

// Convert divs to queue widgets when the DOM is ready
$(function() {
    // Setup html5 version
    $("#html5_uploader").pluploadQueue({
        // General settings
        runtimes : 'html5',
        url : 'upload.php',
        max_file_size : '2000mb',
        chunk_size : '1mb',
        unique_names : false,

        // Specify what files to browse for
        filters : [
            {title : "Video Clips", extensions : "mov,avi,mpg,flv,mp4"},
            {title : "Audio Files", extensions : "mp3,wav"},
            {title : "Executable Files", extensions : "exe"},
            {title : "Zip Files", extensions : "zip,rar"}
        ],
        preinit: attachCallbacks
    });

    // attach callbacks for FileUploaded and Error
    function attachCallbacks(uploader) {
        uploader.bind('FileUploaded', function(up, file, response) {
            response = jQuery.parseJSON( response.response );

            alert(response.error.code);

            if (response.error.code == '500') {
                alert (response.error.message); 
                //alert (file.id);          
                $('#' + file.id).attr('class', 'plupload_failed').find('a').css('display', 'none').attr('title', response.error.message);
                file.status = plupload.FAILED;
            } else {
                alert("yoohoo");
                $('#' + file.id).attr('class', 'plupload_done').find('a').css('display', 'none').attr('title', 'Success');
                file.status = plupload.DONE;
            }
        });
    } 
});

Thank.