Your Themes Fail to Load

When I try to install several of your themes, this is the same message that I get:

"Installing Theme from uploaded file: 148751_wpmu-dev-dashboard-3.2.5.zip
Unpacking the package…

Installing the theme…

The package could not be installed. The theme is missing the style.css stylesheet.

Theme install failed."

Can you please tell me what to do, I am on a deadline and counted on the reliability of your products.

I have installed the latest version of WordPress as prompted to by WP when I logged in. The other theme that failed was:
"Installing Theme from uploaded file: 148751_membership-3.4.2.zip
Unpacking the package…

Installing the theme…

The package could not be installed. The theme is missing the style.css stylesheet.

Theme install failed."

Please send me a response ASAP!
Thanks, Richard