ftp upload

I'm trying to upload a file to a ftp server with the following code
(modified from mozblog).

function uploadFile()
{
	var ioService = Components.classes["@mozilla.org/network/io-service;1"]
		.getService(Components.interfaces.nsIIOService);
	var url = Components.classes["@mozilla.org/network/standard-url;1"];
	fileurl = url.createInstance(Components.interfaces.nsIURL);
	fileurl.spec = "file:///home/sco/polom.html";

	var srcChannel = ioService.newChannelFromURI(fileurl);
	var remoteUrl = url.createInstance(Components.interfaces.nsIURL);
	remoteUrl.spec = "ftp://sco:[email protected]/downloads/polom.txt";
	var ftpChannel = ioService.newChannelFromURI(remoteUrl)
		.QueryInterface(Components.interfaces.nsIUploadChannel);
	
	var bufferedStream =
		Components.classes["@mozilla.org/network/buffered-input-stream;1"]
		.createInstance(Components.interfaces.nsIBufferedInputStream);
	bufferedStream.init(srcChannel.open(), srcChannel.contentLength);
	ftpChannel.setUploadStream(bufferedStream,null,-1);
	ftpChannel.asyncOpen(myListener(), null);
}

Calling that function gives me the following error:

uncaught exception: [Exception... "Component returned failure code: 0x8000ffff (NS_ERROR_UNEXPECTED) [nsIChannel.open]"  nsresult: "0x8000ffff (NS_ERROR_UNEXPECTED)"  location: "JS frame :: uploadPic.js :: uploadFile :: line 15"  data: no]


I'm a little lost there, so any help/hint/lead is welcome.

-- 
Gilles