[Zope] How to debug access denials?

I have problem with Zope security model and I would like to know the best way to debug Zope when access is denied. I have two experimental sites: on one of them, anonymous users can go everywhere. On the other, the permissions *look* exactly the same but anonymous users can only see the home page and are denied access to subfolders (more precisely, Zope asks a password). I assume one DTML method, in the second site, is doing something forbidden (anonymous has "View" and "Access content information"). Is there a way to get an extended log, such as "anonymous user denied because index_html called standard_html_header which called getData and getData is a database connection and they don't have permission to use database connections"?