Solution
I had the same problem, i.e. taskmgr wouldn't open by Ctrl+Alt+Del, and got the same error when using run and noticed my computer was a lot slower than normal and my battery was lasting a shorter time.
Try going into C:\WINDOWS\ServicePackFiles\ and in the folder there should be a task manager icon which opened the manager for me. (If you don't have it,
you could try the long process of removing SP2 and reinstalling it to get it.)
Interestingly, my CPU usage is contantly 100%, 98% of which is winupdates.exe. Ending winupdates.exe immediately gave me control of task manager via Ctrl+Alt+Del and immediately ending the process my CPU's fan went down 2 levels.
Hope that helps,
Kyle.
(kyle.strachan@blueyonder.co.uk)