That happened to me before too, I had to change to a different e-mail account. But I continued getting my notices once I did. This happens every once in a while, where I stop getting notices for some threads but still get them for others. Then it occurs to me that I haven't seen anything from a thread in awhile, and then I go check it out. Once I add a post to it, I will start receiving them again. It is a little frustrating.