Same problem, and no response from Microsoft ? :-(
It had worked earlier, so what happen microsoft ?, and what is the solution to this issue ?
I believe a recent update must have disabled this for some reason. The solution is to disable HideFastUserSwitching.
Open regedit.exe and navigate to ->
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\
Set HideFastUserSwitching to 0 and it should reappear.