I don’t know if this is going to be the same for everyone but…
I’m running Ubuntu Desktop (8.10). I had developed the basics for a new theme on my main computer (also Ubuntu Desktop 8.10) and had transferred the theme files to my working laptop via jump drive. I maintain my web development in www/*projectfolder*. I had to change “Other” permissions to “Access Files” on the theme folder I had transferred into wp-content/themes. You have to set the permissions to “access” (at the very least) otherwise the web server can’t see the folder.
I don’t know what kind of scenario might or might not exist which would be similar for a windows system or if someone has linux but a different permission scheme, but that’s what had to be done in my case.
I was using just file transfers on the OS, not WP’s upload/import functions.
p.s. Might also need to apply (at least) a “read-only” to (at least) the “style.css” otherwise wordpress reads the theme as broken.