I can't upload files from html form on my node/express app

Ok, It’s actually Jimp that is cause the problem here. I was trying to resize the file before saving, and it’s failing somewhere here:

function savePhoto(photo, userId) {
    var timestamp = Math.round((new Date()).getTime() / 1000);
    var photoname = userId + - + timestamp + '.png';
    jimp.read(photo.data, function (err, photo) {
        if (err) throw err;
        photo.resize(400, jimp.AUTO)            
            .quality(70)
            .write("public/uploads/" + photoname);
    });
    return photoname;
}

whereas if i use ‘express-fileupload’ to save the file, it works fine:

function savePhoto(photo, userId) {
    var timestamp = Math.round((new Date()).getTime() / 1000);
    var photoname = userId + - + timestamp + '.png';
    photo.mv('public/uploads/' + photoname, function(err) {
        if (err) throw err;
    });
    return photoname;
}

Thanks for any help!