I have to agree with the others that it isn't a black tie appropriate dress - at least for any black tie event that I've been too.
If you're going to add a cardigan it will cover you up but the dress will also look more casual IMO. I also just don't think its work appropriate - keep the dress and get something more sophisticated for the work event, you want people to remember that you looked sophisticated and well-put together, not necessarily what dress you wore.