If you get this message on your PC, stating that the Task Manager is disabled by administrator, you can correct this error by enabling it from the Registry Editor.
To do so:
Click on "Start" menu and then select and click on "Run"
In the "Run" window type "regedit" and click on "OK"
In the "Registry Editor" window that opens, navigate to:
My Computer \ HKEY_CURRENT_USER \ Software \ Microsoft \ Windows \ CurrentVersion \ Policies\ System
In the right-pane, right click and delete the value, "DisableTaskMgr" [Deleting this value from the Registry Editor would make sure that the task bar remains enabled at all times]. Close the Registry Editor.