All screenshots and no gists makes James unhappy.

gistfile1.txt

var renderError = function(res, error) {
	res.status = 404;
	res.render('error', {
		title: 'Error',
		error: error
	});
};

exports.findWithId = function(req, res) {
	var Article = mongoose.model('Article');
	Article.findById(req.params['id'], function(err, article) {
		console.log(err + " " + article);
		if (err) {
			renderError(res, err.message);
		}
		else {
			if (article == undefined || article == null) {
				renderError(res, "No article with id " + req.params["id"] + " exists.");
			}
			else {
				renderSuccess(res, article);
			}
		}
	});
};

Arrggh, had a huge comment but fucking Preview button did something weird and deleted my comments

in short, you should specify some error handler function as mentioned here :: http://expressjs.com/guide.html#error-handling

and then in your function just call next(err) with some error message

exports.findWithId = function(req, res, next) {
    var Article = mongoose.model('Article');
    Article.findById(req.params['id'], function(err, article) {
        if (err) {
            return next(err);
        }
        if (article == undefined || article == null) {
            return next(new Error("No article with id " + req.params["id"] + " exists."));
        }
        renderSuccess(res, article);
    });
};