[Zope] exUserFolder: short error-message showing up prior to login form

Hi, using exUserFolder with Cookie based authentification (basic and secure) and database based auth.source an error message shows up for one or a half second before the login form appears and everything works as normal afterwards. This happens with the standart form or a customized one. It doesn't look very good so I want to stop that. Any clues about that? I cannot read that fast to tell you about the content of the error message. -- Elena