When I was trying this the night you originally posted, I was getting the same error. And like you already observed, i stripped the script down to the bare minimum (basically just a shutdown command) and it still failed (believe I was getting error 53 ?!) ... also tried the shutdown.exe command and no worky ...

There is something in Windows XP that is blocking or denying the shutdown but cant for the life of me figure it out ... we have a similar scheduled job running under Windows NT ... just does a shutdown/restart at 2:00am every morning but it runs under the AT scheduler not task scheduler ... would be interested in knowing if this same problem appears under the AT command on Windows XP. If yes (or no) not sure what that would say or mean ...

-Shawn