Task Manager Disabled

Error: Task Manager has been disabled by your administrator
Error: Registry Editing has been disabled by your administrator

Microsoft Solution: Start > Run > gpedit.msc > Group Policy settings > User Configuration > Administrative Templates > System > Ctrl+Alt+Del Options > Remove Task Manager > Remove Task Manager
Microsoft Solution: Modify your registry

[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System]
  "DisableTaskMgr"=dword:00000000
[HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Group Policy Objects\
LocalUser\Software\Microsoft\Windows\CurrentVersion\Policies\System]
  "DisableTaskMgr"=dword:00000000
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System]
  "DisableTaskMgr"=dword:00000000
[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\WindowsNT\CurrentVersion\Winlogon]
  "DisableCAD"=dword:00000000

But i think that you fall in virus Nice Trojan 2.0 (Trojan-Spy.Win32.VB.cs)
if you have NDDEN.EXE (c:\WINDOWS\NDDEN.exe) then you have a Persian Virus.
Here is the virus specifications:
Owner: Javad.M
Written: Visual Basic
Date: September 2004
Country: Persia(Iran)
File: C:\WINDOWS\NDDEN.exe
Size: 23,567 bytes
Registry:

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
  "disableregistrytools"
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System
  "DisableTaskMgr"
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  "Microsoft PCHealth32"