Unable to change login screen

[Unevolved]

Whenever I try to change the login screen in Hardy, I get an error message saying the file I'm attempting to add is not a tar.gz file, which it obviously is:

http://i284.photobucket.com/albums/ll35/unev0lved/Screenshots/screenshot1-1.png

Any thoughts? Its been doing this for a while, and I'm pretty sure the theme files have login screens. Would that cause it? It's done this with any I try.

Thanks in advance.