Double check the permissions on the simpla folder, compare the default theme to the simpla one to make sure.
Also, I'll add, that despite my daily FTPing of WordPress files, I inadvertently spent about 45 minutes today trying to figure out a similar issue. I then realized that I was in fact uploading the files to the wrong directory on the domain. I mean I tried a different FTP client, a dozen themes, nothing seemed to work. Then to my embarrassment, I was uploading to an install of WP at the root of the domain, and not the subdomain that I was navigating to in my browser, and intended for the theme to be. Moral of story, double check the path in your FTP.