Hi,
I'm stuck with this same problem, and none of these suggestions work for me...
* Pressing Ctrl-Alt-Del on the OSK brings up a popup saying
"To use the commands available when you press Ctrl+Alt+Del, click on your user tile and choose an option."
And when I click on my user tile, the only options are "Lock" and "Sign Out".
* The net user command fails with the message:
"Access is denied".