As a test I just now downloaded the 4 disks yet again and ran them through the 7k and they all passed so there is nothing wrong with the download. There is no mention of the version you were upgrading from. Try running disks 3 and 4 first then disks 1 and 2. A failure is most likely a corrupt disk, thus use new disks and format them in the 7k for safety even though this is not strictly necessary. There is nothing lost and everything to gain in doing the checksum several times for safety if using older disks. Switching off or not finishing during an actual upgrade run is a very bad sign.