You already know the reason: a change (update, etc) in Windows 10 Preview is the culprit.
If you enter in Google "Virtualbox has terminated unexpectedly during startup with exit code 1 (0x1)" then you'll get hundreds of founds. There all posters confirm that it's not the VirtualBox VM, but Windows OS. Suggest you to ask your question in a Windows OS related forum. First thing of all things I'ld do is return to the system restore point Windows created before it made changes.
True is that Oracle starting with VirtualBox 5.0 improved Windows 10 support.