Task Scheduler Error 2?

I was going to run the prefetch optimisation that Ive run before with no hassles on my media center. It Windows XP MCE 2005 thats been fully updated. I went to start the task sheduler and got this error:

Could not start the Task Sheduler service on Local Computer.

Error 2: The system cannot find the file specified.

I tried to run the SFC but it keeps saying that the wrong cd is in the dirve even though its the installation CD.

Ive found a similar reference to this error that was in Windows ME but this was to do with the renaming of the harddisk.

Any ideas?

Aquagraphite