I just upgraded to 3.7 on a couple of non-essential sites (cleared caches, disabled all plugins, backed up database + files, made sure none of the plugins are the ones mentioned in the Master List post), and for some reason now any WordPress files stored in /wp-admin/ are inaccessible.
For instance, upon finishing the update, I click on the "Return to updates" page, which should bring me to mydomain.com/wp-admin/update-core.php, but when visiting that page, I get the standard WordPress 404 error page, with my site's theme. Similarly, going back into the dashboard and clicking on the Plugins tab should bring me to mydomain.com/wp-admin/plugins.php, but instead I get the same 404 page.
I can confirm that all the files are actually on the server (and are their most updated versions). Any advice?