Recently upgraded from Snow Leopard to Mountain Lion. All went well, installed correctly ran lovely, then the software update screen pops up saying there is a 1.7GB update for the OS, downloaded it, installed ok it then rebooted the system and promptly crashed after the white screen and the music with what looked like a list of register values and a an error message. Hmmm... Restored the computer from a TimeMachine backup, went through the same process, installed fine, message about the 1.7GB update, installed ok reboots computer crashes. Questions are: What causes this? How can I skip past the corrupting update and get any later ones?