why my ajax mootools method keeps showing me an Error alert?

I am trying to make a simple upload file system, and this is my code , I hope you can help me, help very appreciated

init.php

   <form method="post" action="" enctype="multipart/form-data">            
            <label for="file">Upload a file</label>
            <input type="file" name="file" id="fileArchivo" />
            <input type="submit" name="submit" id="btnUpload" value="Upload file" />   
        </form>

Ajax mootools method

window.addEvent("domready",function(){
    cargarIndex();                                
});


function loadIndex()
{   
   var Request = new Request({
   method: 'POST', 
   url: '../CONTROLLER/init.php',
   onRequest: function() {}, 
   onSuccess: function(text, xmlrespuesta){
   document.getElementById('archive').innerHTML= texto;
   $('btnUpload').addEvent('click',function(){uploadFile()});  
   },
   onFailure: function(){alert('Error!');}  
   }).send();


}

function uploadFile(){
//$('btnUpload').addEvent('click', function(){
    alert('in');
    archivo = $('fileArchivo').value;
    alert(archivo);
      var nuevoRequest = new Request({  

           method: 'POST',
           data: 'archivo='+archivo,
           url: '../CONTROLLER/controllerSave.php',  
           onRequest: function() {$('subirarchivo2').innerHTML="Cargando...";},
           onSuccess: function(texto, xmlrespuesta) {$('subirarchivo2').set('html',texto);},
           onFailure: function(){alert('Error!');}                                                 
           }).send();           
//});
} 

Firebug says that uncaught exception:

[Exception... "prompt aborted by user" nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)" location: "JS frame :: resource://gre/components/nsPrompter.js :: openTabPrompt :: line 468" data: no]

But I dont get the answers, I already search but nothing, the Error alert is in the onFailure in the uploadFile.

can't use ajax like so to upload files.

http://mootools.net/forge/p/form_upload by core member Arian

http://mootools.net/forge/p/uploadmanager by Thiery Bela

Both provide sensible solutions via HTML5 interfaces with a flash uploader fallback / degradation for older browsers.