I encountered a strange problem in one of my schools this morning, scenario is server 2008, Window 7 SP1...anyway, if I log in as pupil then try to log off the pc looks like it is going to log you out but then it just displays a black screen although I can still see the mouse and move it around the screen.

I cannot access task manager etc so have to power it off to regain control, if I log in as an administrator or a teacher it works fine.

I can also connect to the pcs (it is every one in the suite) using AB Tutor and reboot them.

I am at a loss as to what this could be as nothing has changed on my group policy and I haven't installed any new software.