Policy Not taking effect

When implimenting policies on workstations I am finding that some of the policy options are being accepted while others are not, or some computer accept the full policy, my biggest problem has been disabling the logoff button, taskbar button, and shutdown button from the “ctrl-alt-delete” screen. I am using policy editor to make these changes however it a 50/50 shot on which computers are accepting the policy the other are not affected. Please let me know if you have any suggestion as to what Imight be doing wrong

Thanks
Chris
Systems Administrator