I had a different problem. I was using a theme called “55”. i uploaded the theme to the correct place but it just would not show up. I dug around a bit and it looks like WP (at least my v2.7) has problems seeing themes whose names are numbers. I changed the theme name to actual words (say “My Niche Blog Theme”) and now it works fine. To change the theme name, I had to edit the file style.css and change the comment at the top.
Not sure why this works, but it does. Hopefully this will help someone else who has had problems getting a number-named theme to show up in the Manage Themes area.
