I attended Microsoft’s Build Conference last week. This was for their Windows 8 rollout.
They gave every attendee a Surface tablet device and a Nokia 920 cellphone to help seed the development tools.
One of the things I encountered was trying to add additional users to the tablet, was that the user you were trying to add needed to be logged into the Microsoft ecosystem.
was trying to add an account we use for testing; I was able to add it okay, but I couldn’t sign int the tablet using the credentials until I had actively logged into the Live account associated with that user on another machine.