I previously installed the first beta of High Sierra and all went well on my MBP 2011. I hadn't used it in a while and woke it up yesterday and instead of being on the desktop, a windows was displayed stating "macOS could not be installed on your computer" "The path /System/Installation/Packages/OSInstall.mpkg appears to be missing or is damaged". My only option is to click restart and a progress bar appears and goes for a while and then I get the same thing. I was stupid enough not to make a Sierra USB stick before installing the beta. How can I get my machine bootable again?