A strange behaviour we recently bumped into was that the "CreatePage" action redirect a user to the "Access Denide" page eventhough this user is a member of the site contributors.
In order to solve this situation follow these steps:
1. Go to Site Actions -> Site Settings ->Modify all site settings
2. Go to Galleries -> Master pages and page layouts
3. From the list toolbar, select Settings -> Document library settings
4. Select permissions for this document library
5. Add 'Restricted Read' access to the required groups
9 months ago