Save that file as a backup
(all you have to do is change the name to taskmgrccs.reg and doubleclick it to get the old values back)
Then copy the part in bold below into notepad and save it as taskmgrrem.reg
Set Filetype to "all files"
Doubleclick that file and confirm you want to merge it with the registry.
Then reboot and try both doubleclicking taskmgr.exe and using Ctrl_Alt_Del
Let me know what happens.