[Zope] Z2.log logs user as Anonymous

Hi, I've got CookieCrumbler installed with my Zope site in order to carry out user authentication. My users can initally register to the site - they are added to the acl_users folder in this step. From then on they can log into the site as registered users.... all works fine till here. The only problem is with my Z2.log... the zope access log. I'd like to use this to gather some statistics about which users log in most frequently etc. What's happening though is that when a user logs into the site and continues browsing through it, the z2.log keeps logging the user as "Anonymous". The only time this changes is when I use the ZMI and in that case the log lists the user as 'admin'. Can anyone tell me what I'm missing? Cheers Ruth