scheduled task shutdown on XP

I'm attempting to use a scheduled task to shut down my win XP PC. I get the error: Task Scheduler Error 0x80070005: Access is denied. I'm logged in with administrative privileges but am unsure why the task isn't starting or won't work. I don't know what I'm doing wrong. Can anyone give me some pointers please?

Incidentally, as a work around, I have managed to get around this whole thing with a batch file on a timer.

OK, I have just tried this myself, and it has worked. So just checking if you have the correct settings, here is a screenshot of my settings. Note: I am using Windows Vista, but shouldn't make any difference.

General Tab:

Your batch file (for Windows XP) will only need the following line of code:

shutdown.exe -s -t 00