Problem: When creating a page in SharePoint 2007 a user that is part of the members group (or another group that has proper permissions on the pages library) receives an access denied error message.
Possible Solution: Check the permissions of the master page document library to ensure that the users creating pages have at least read access to the files. In our case we needed to make sure that the members group had read access.
Possible Cause: In our situation we had taken a subsite and redeployed it as a site collection in a new web application that was enabled for anonymous users. This caused the master page gallery permissions to be inaccurate. Once we fixed the permissions in the master page gallery the users in the members group could now create pages.