After installing Windows 10, I changed my Administrator account password, losing my EFS-encryption on some system files according to this fine print which I didn't read in my haste to make sure I had a working password:
Now, I can't downgrade because it keeps giving me the error when trying to downgrade that I need to remove Administrator (even though I restored its de-activated state through "net user Administrator /active:no" command).
If anyone has any solution at all... I will try anything.