From: probgoo on
User Security Issues with SharePoint 2007 site(s) with WSS 3.0
We have one main site with many sub-sites under it. When we add a
user to a sub-site (Member, Visitor, Owner) the user cannot get into
the site unless they are then added to the main site (Member, Visitor,
Owner) and get an Access is Denied right upon login. Adding the user
to the Main site fixes it well enough, but then the user sees other
sub-sites that they aren't even added to as a Member, Visitor or
Owner. This may be poor design on our part but there seems to be no
way around having all users be Visitors (or higher) to any Main site
you have if you want them to see some or all of any sub-sites.