This usually means that the permissions of your site's root do not allow file listings. Please change the permissions of your site's root to 0755 or higher. If unsure how to do that, please ask your host; we don't know how each and every host works. You may also ask your host to give read and file listing permissions to your web root. They will either do that for you or tell you exactly how to do that.
On some hosts, we saw that it was necessary (on top of the above) to give 0755 permissions to the backup archive and all of its parts if any exist, e.g. file.jpa, file.j01, file.j02 etc. I know, this doesn't make any sense (0644 permissions on the file should work!) but it looks as if some hosts are grossly misconfigured. So, try setting your site's root directory permissions to 0755 and the permissions of your backup archive to 0755 as well. Kickstart should be left with 0644 permissions or you risk getting a 500 Internal Server Error.