When trying to start Task Manager in Windows, you will receive the following error:
Task Manager has been disabled by your administrator.

I’ve seen this within company environments, where it was caused by a group policy setting:
User Configuration\Administrative Templates\System\Ctrl+Alt+Del Options\Remove Task Manager

Last week I was at a BBQ of a buddy of mine, where his father had a laptop and was experiencing the exact same issue. Since this laptop was not member of a domain and no policies were applied, changing the correct registry value to “0” was the solution:
HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\System\disabletaskMgr