Issue:
User has Full Control on a Sub-Site but when he try to edit any page in this site SharePoint show Access Denied message.
Reason:
User doesn't have access to master page gallery
Solution:
Navigate to Site Collection Settings >> Galleries >> Master pages (http://server_name/_catalogs/masterpage/Forms/AllItems.aspx)
Then to Library Settings >> Select Permissions for this document library
On permissions page check if SharePoint Group "Style Resource Readers" has Read permission (This group contains "NT AUTHORITY\Authenticated Users" )
User has Full Control on a Sub-Site but when he try to edit any page in this site SharePoint show Access Denied message.
User doesn't have access to master page gallery
Navigate to Site Collection Settings >> Galleries >> Master pages (http://server_name/_catalogs/masterpage/Forms/AllItems.aspx)
On permissions page check if SharePoint Group "Style Resource Readers" has Read permission (This group contains "NT AUTHORITY\Authenticated Users" )