Question : Switch user problem

I was previously able to switch user without logging off. Since yesterday this function stopped working. I tried to reactivate it in control panel- User Account - change the way users logs on or off. I ticked the fast user switching check box then apply option but this did not work. When I went back in the  "change the way users logs on or off" dialog box the check box was unticked. I have tried many time and the tick won't stay on.

Please advise

Cheers

Answer : Switch user problem

The service is called "Fast User Switching Compatibility"