After I imported some new PageTypes, an user that is not logged in to the site receives the loginform for evry request.
All pages have the role "Everyone" set to "Read". This is strange I think.
If I create a new user and don't put it in any roles nor give it any privliges, I can log in with that user and browse the whole site.
Anybody seen this behaviour before?
Problem solved. IUSR was not added to webroot. This worked earlier, but for some reason needed it now.