That's what I was doing but you can't zip the whole folder but instead the contents (100%,200% etc)
So now I've got the theme to show up but I get this:
It appears the contents are all there, xml file, ini file sub folders etc.
Oh well. The Modern theme is great. I just like to edit themes to my personal taste and I've done so for dozens of plugins that allow skin editing but with a great deal more success.