In a sharepoint.com trial site, for my root site collection, I can't upload master pages (or anything else for that matter). I tried deleting the root site collection and re-creating it as a publishing site, but I keep getting the same error: Access denied.
I can access the Master Page Gallery just fine, and in the Files tab of the ribbon, choose either New Document or Upload Document. However as soon as I select something, I get "Sorry, you don't have access to this page". I have site collection admin, and am in the site owners group.
I have tried requesting permission, and granting myself full control. I also went to the library settings of the master page gallery library and tried from there. I also can't open the root site collection in SharePoint Designer, I get a 403 Forbidden response. I am able to do this on other non-root site collections, just not for the root site colleciton.