You are an anonymous user to Nabble. Anonymous users can do a lot of things, but not everything. Since you didn't register, Nabble identifies you by reading a cookie in your browser. This is not good because Nabble can't identify you if you use another browser or computer. So you must register and log in -- this will make it easier for Nabble to identify you by email.
http://n2.nabble.com/user/Register.jtpRemember that Nabble doesn't have your email and can't notify you about things that happen to your forum.