This week I had a strange issue in Remote Tools. Everything was working fine on the ConfigMgr client, and Remote Tools for it seems also. But when starting the "Send Ctrl-Alt-Del Key" nothing was happening. Strange issue, never seen that before! The solution for this is not that hard, because other people has already found a solution for it. As far as I know a GPO is blocking this functionality.
Just create or edit a Group Policy, browse to Computer Configuration, Policies, Administrative Templates, Windows Components, Windows Logon Options. In there enable the setting "Disable or enable software Secure Attention Sequence" and configure it on "Services and Ease of Access applications". After a GPupdate you will see the "Send Ctrl-Alt-Del Key" is working (again)! Happy again :-)
Source: Microsoft TechNet