Well, we had a look and on our system there is a clear cut problem. When you register a new user you are creating a Member object. The form for the new registration only shows a handful of attributes. A vast majority of attributes are not shown on the form - yet some of them are defined as "value must be provided" and so there is a problem.
On our system the Tomcat log says "Operation error. Value of Profession must be provided". The reason is that Profession attribute is undefined. Unfortunately the error message is not displayed on screen, but we are working on it.
