Can’t change theme name

From what you are describing, the ASCII is being incorrectly converted when you upload the file via FTP.

Go to WP-Admin and select Appearance -> Editor. Look at Style.css, does it look like it’s been minified in a really strange way? If so, you have a problem with the UTF encoding on your end. It’ll get a lot nastier if this happens to a core file like single.php.

In Filezilla, change your transfer type to “Binary”, re-upload, and see what happens.