SWFUpload

I am using swfupload as a file uploading option in my form like classic form demo http://demo.swfupload.org/v220/formsdemo/index.php but it should not be mandatory to upload the file . in my form only subject (a text field of my form) is mandatory

my handler.js file looks like ( validform function i think its responsible for validation )

function validateForm() {
var txtSubject = document.getElementById("subject");
var txtFileName = document.getElementById("txtFileName");

var isValid = true;

if (txtSubject.value == "") {
isValid = false;
}

document.getElementById("btnSubmit").disabled = !isValid;

}

//
though this enables the "submit button" of the form but form is not working if i click on submit button it goes nowhere . it does not execute upload.php(actually check.php) page .. it does nothing..

my settings are like >

var swfu;

window.onload = function () {
swfu = new SWFUpload({
// Backend settings
upload_url: "<?php echo DIRECT_URL; ?>SWFUpload/check.php",
file_post_name: "txtFileName",

// Flash file settings
file_size_limit : "10 MB",
file_types : "*.flv", // or you could use something like: "*.doc;*.wpd;*.pdf",
file_types_description : "All Files",
file_upload_limit : "1",
file_queue_limit : "0",

post_params : {
PHPSESSID: "<?php echo session_id(); ?>"
},

// Event handler settings
swfupload_loaded_handler : swfUploadLoaded,

file_dialog_start_handler: fileDialogStart,
file_queued_handler : fileQueued,
file_queue_error_handler : fileQueueError,
file_dialog_complete_handler : fileDialogComplete,

//upload_start_handler : uploadStart, // I could do some client/JavaScript validation here, but I don't need to.
upload_progress_handler : uploadProgress,
upload_error_handler : uploadError,
upload_success_handler : uploadSuccess,
upload_complete_handler : uploadComplete,

// Button Settings
button_image_url : "<?php echo DIRECT_URL; ?>SWFUpload/XPButtonUploadText_61x22.png",
button_placeholder_id : "spanButtonPlaceholder",
button_width: 61,
button_height: 22,

// Flash Settings
flash_url : "<?php echo DIRECT_URL; ?>SWFUpload/swfupload.swf",

custom_settings : {
progress_target : "fsUploadProgress",
upload_successful : false
},

// Debug settings
debug: false
});

};

I have attached my form and handler.js file .. hope this is sufficient to fix the problem.