Unable to Upload *any* Theme

Whenever I try to upload a WordPress theme (i.e. from my desktop) I am given this error message: “Incompatible Archive. PCLZIP_ERR_BAD_FORMAT (-10) : Unable to find End of Central Dir Record signature”.

I don’t know what’s up here. I think the problem is that I’m not uploading a .zip, I’m forced to choose one thing in the theme folder so I choose style.css

What’s going on here? Is it the themes? Is it me? Is it both?

Thanks! -Gabi