For all those that were not aware the deadline is soon approaching (December 31, 2017) for the last free upgrades from Windows 7 to Windows 10:

Windows 10 upgrade for assistive technology users

Microsoft: Final Free Windows 10 Upgrade Offer Ends Dec. 31 | News & Opinion |

For failed upgrade attempts this is a troubleshooting step that has fixed many upgrade failures:

replace: C:\Windows10Upgrade\wimgapi.dll
with: C:\Windows\System32\wimgapi.dll