Need IT help (remote shutdown of Win7 computer)

I need some IT help at Astrokolkhoz.

The local network of observatory computers can be shut down with a single BAT file...using the   shutdown    command....

...except for one stubborn computer.  (Win 7 Home Premium 32-bit)  It gives the not-very-informative error message:  Access denied (5).

I've got plenty of XP machines, and one or two Win 7 64 bit Home Premium machines that respond properly to a remote shutdown command.

Why does this one computer refuse to work?  (I'm the administrator and sole operator of all of them...set them up all the same way, etc.)

If you have any ideas on how I can troubleshoot and fix this issue, please tell me how I can peer inside this black box that only says  "Access denied (5)."  (If I knew it was a registry entry...I'd change it in a heartbeat...but I'm fumbling in the dark on this issue.)

Thanks in advance.