Well... I downloaded again and used 7-zip to open it. Files were extracted but an error message showed up and said "this file is broken" and an extracted .sff file is 0KB. I used 4 browsers to download, IE, Firefox, Chrome and Opera, but I got the same results. A file I downloaded is about 40KB but I think it should be more than that.
It might be a temporary server problem if you can open and use it as a stage in Mugen without troubles.