I will get a message that "that action is not allowed" when I am typing a longer response to a posting. So what I have learned to do is simply copy what I have just wrote. Get out of the forum, then log back in, find the post I was responding to, hit reply, paste my response back in. It is a number of steps but is quicker than re-typing everything back in and trying to remember just what it was that I was posting.
or maybe the message is "you do not have permission to do that action" I can't remember exactly what the message is.