File permissions, can't delete file with 0 bytes size

I downloaded a file, didn't download correctly, size = 0 bytes. Reports owner unknown. I can't change ownership, remove file properties, any of that stuff. Can't rename or delete. I'm logged in as administrator but it keeps asking for administrator permission. ?? Another question about file ownerships - I tried to do a backup once, during an OS re-install, many files came back garbled,...