We have discovered a database error on All The Tropes that is preventing us from deleting some but not all unused files. The files in question have all been uploaded more than once, with no thumbnail available for the first version uploaded.
So far, we have discovered 468 of these files, all of which are listed at https://allthetropes.org/wiki/Category:Undeletable_files
Please delete the files listed there via the database backend. Please do not delete the category page - we are still going through the old files and identifying some that are not being used and do not have CC licenses.