Maybe you did so many and maxed out the number of offers you can do. That happen to me and when I complained to igg they said there is a certain amount of free IM points you can get. If you go over the limit do so at your own risk. They should post somewhere how many offers you did and what the max is so we don't waste our time doing it and get message saying "sorry you reached the limit, all offers you do is at your own risk".