Seems that Windows 10 periodically (secretly) resets the "
fast shutdown" feature to "ON". This has the effect of leaving the hard drive in a state of
hibernation that precluded Ubuntu from booting.
Since it does not happen often, I forget how to solve this issue. So I spent a couple of fun filled hours dwelling on this. A tutorial concerning how to fully shutdown Windows 10 is located here.
How to fully shut down windows 10.
That solved the problem and Ubuntu once again boots successfully.
