If the MD5 matches then the download is fine (although you should always use the torrent as tk says, it will always be much more reliable). But if the download is fine, then the next port of call is the burn. Because the content is predominantly a single, very large, monolithic file it is particularly susceptable to a fatal error during burning. It is absolutely critical to burn on the slowest speed (ideally 1x) with decent media, to be able to rule out burn errors.