Themes will not install

Brian Purkiss of your Customer Support Team advised me to submit the following issues to you. Please help me.

Message: 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 for your help,
Richard