Mint Display Manager refused to install a new theme?

[LinuxMintKid]

Hiya! I'm trying to install a new theme to the Mint Display Manager and I am having techincal difficulties. When I attempt to install a GDM theme (Note that I have done the prior config to the .desktop file changing it from GdmGreeterTheme.desktop to MdmGreeterTheme.desktop and the files data [GdmGreeterTheme] to [MdmGreeterTheme] and removing the extra .desktop when it's modified.) It gives me this window here.

Not a theme archive.
File not a .tar.gz or tar archive

And I've put it through tar.gz and .tar (The two recommended formats.) I will try .bz2 and .bz and .tgz and see if I have sucess with those. If I do I will solve this.

[LinuxMintKid]

Guess what it only works with .tar and .tar.gz sooo... does anyone know whats worng?