Cordova's FileTransfer Writing Error (Code 1)

I'm using Cordova 4.2.0 for Android.

I have some troubles to get FileTransfer plugin work properly. I suppose that there is a writing error

exception:".myApp\/contentImages\/20150110220101.jpg: open failed: ENOENT (No such file or directory)"

filename was previously tested and does not exist yet:

rootFS.getFile('.myApp/contentImages/'+file,{create:false},
    function(){
        console.log(file+' already exists');
    },
    function(error){
        console.log(file+" does not exist locally");
        console.log("Error #"+error.code);
        download(file);
    }
);

And here is the download function:

function download (filename){
    var localPath = rootFS.fullPath+'/.myApp/contentImages/'+filename;
    var fileTransfer = new FileTransfer();
    fileTransfer.download(
        encodeURI('http://distantApp/contentImages/'+filename), // This file exists
        localPath,
        function(entry) {
            console.log("download complete: " + entry.fullPath);
        },
        function (error) {
            console.log('download error: ' + error.code + ": "+error.exception+" ; source " + error.source+" ; target " + error.target);
        }
    );
}

What could be the problem?

EDIT Code for rootFS

function onDeviceReady(){
    window.requestFileSystem  = window.requestFileSystem || window.webkitRequestFileSystem;
    window.requestFileSystem(LocalFileSystem.PERSISTENT, 0, gotFS, function(){
        console.log("error requesting LocalFileSystem");
    });
}
function gotFS(fileSystem) {
    console.log("got filesystem: "+fileSystem.name); // displays "persistent"
    console.log(fileSystem.root.fullPath); // displays "/"
    window.rootFS = fileSystem.root;
}

The problem was caused by an upgrade of Cordova from a previous version.

The path of local files was not properly identified: .fullPathis now obsolete and should be replaced by .toURL().