New
#30
In any version of Windows, if you move one user profile or them all, you have to use the same method to move them back to C: before upgrading.
If you Sysprep users to X: (Vista to Win10 Build 9860), you have to use the same method to move them back. Then you can upgrade without issues. See this tutorial, the Upgrade section at the end of it for more information.
The same if you use the registry. You have to edit the registry to put users back to C:, then upgrade, and again move them to another drive.