I get the same error message. I installed my virtual box and appliance in windows 8.1 and it worked perfectly with windows 8.1. After the upgrade without changing anything else, it doesn't work anymore.
Error text: The virtual machine 'CS50 Appliance 2014' has terminated unexpectedly during startup with exit code 1 (0x1). More details may be available in 'C:\Users\Seagal\VirtualBox VMs\CS50 Appliance 2014\Logs\VBoxStartup.log'.
Result Code: E_FAIL (0x80004005) Component: MachineWrap Interface: IMachine {f30138d4-e5ea-4b3a-8858-a059de4c93fd}
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